#24 - The body of anyone infected by virus X will, after a

[reop6780]

This question is "must be true" type, and I chose C for the answer.

First of all, I'd like to know what kind of incorrect answer C is such as "New" information, Shell game...etc.

The way I approached C was based upon the question, "what if antibodies increase in response to other factors other than X?"

Since the test can tell how long that person has had X based upon the number of X, I thought it was important to tell such number is not influenced by none-X factors.

Anyway, the answer is D, which I came to accept that there is no problem with that.

I just cannot tell how C is a wrong answer.

It would be really easier for me to understand if the explanation is related with Must Be True chapter in LR bible.

Thank you.

[Ron Gore]

Hi, Reop!

It's great that you properly identified this question as a Must Be True question. As discussed in the Logical Reasoning Bible, we use the Fact Test to prove to ourselves that the answer choice we select contains only a restatement of one of the facts provided in the stimulus or an inference that is permissible from a combination of the facts. An answer choice that contains new information, i.e., neither a restatement nor a permissible inference from the facts, will be incorrect.

In this question, the facts provided by the stimulus are:

(1) anyone who has had Virus X for at least a week will produce antibodies to fight the virus;

(2) the number of antibodies in the person will increase for the next year or two;

(3) there is a test that can reliably tell how many antibodies are in a person's body; and

(4) if the test is positive (i.e., for antibodies in the person), then it can be used during the first year of infection to determine, within a month, how long the person has had the virus.

The correct answer choice could test you on any of the these facts, or an inference from their combination. The correct answer choice, (E) and not (D), as in your post, is a restatement of the first fact, that after one week of having Virus X, a person produces antibodies to fight it.

Answer choice (E) states that a person will "for a time" fail to exhibit infection using the antibody test. Since a person does not begin to produce antibodies for a week, then during the first week of infection they would have a negative result on the antibody test, despite being infected.

Answer choice (C) is incorrect because it talks about new information not included within the stimulus, and so is only a Could Be True answer, rather than a Must Be True. The stimulus provided no information regarding any of the body's other defenses to infection, nor did it discuss any infections other than Virus X. It is improperly restrictive, based on the evidence in stimulus, to say that antibodies are produced only for viral infections that cannot be fought by any other body defenses.

Your process of testing the facts by means of a hypothetical indicates that you did not constrain yourself to the facts in the stimulus, and perhaps were treating this as a Help or a Hurt Family question, with the bottom-to-top information flow, even though you recognized the question to be a Must Be True, a Prove Family question with a top-to-bottom information flow.

Also, a note on answer choice (D). It is incorrect because the premises told you only that an infected person will continue to produce antibodies for a year or two, and gave no indication that there is no limit to the number of antibodies that could be present in the person's body.

Please let me know if you need further clarification.

Thanks!

Ron

[reop6780]

It was easy to understand since you related the problem with Bible explanation !

Also, thank you for pointing out that i may have confused this question with second family !

[GLMDYP]

Hi! For this question, the right answer is (E). But why is that anyone infected by virus X will for a time fail to exhibit infection if tested by the antibody test? I cannot figure out the logic here. Thanks!

[Nikki Siclunov]

Hi GLMDYP,

The reason why (E) is correct can be found in the first sentence: it takes a week to produce antibodies. So, if you use the antibody test on someone who got infected within a week before the test, the results will come back false negative.

Does this make sense?

Let me know. Thanks!

[bk1111]

Hello - is D incorrect because it is not possible to infer that there is "no limit to the number of antibodies" in a person's body if they are infected with virus X indefinitely? I was between D and E before correctly picking E as the answer. Thank you!

[Jennifer Janowsky]

Hi, bk1111! D is indeed incorrect because there is nothing in the passage to infer that there is not a limit to antibodies in the body. It seems to be possible, according to the stimulus, that the antibodies may maximize after 1 year of infection, which could be why the test only works that long. Regardless, there is nothing about a limit to antibodies suggested. Hope this makes sense!

[kliu49]

Hello! I got answer E, but based my answer off the wrong premise. I did not notice the production of antibodies after a week statement, but rather the last sentence of the stimulus: "If positive, this test can be used during the first year of infection...". Could answer E also be concluded from this sentence? Or would it only be speculation?

Thank you!

[James Finch]

Hi K Liu,

We can infer that the test may not be accurate a year or more after infection by what is stated in the last sentence, but it doesn't actually go as far as what is said in (E); it may be inaccurate because it shows false negatives, as (E) is saying, but also because it shows false positives, since we aren't told how long the antibodies stick around after the virus has been defeated. So only the first sentence actually supports (E).

Hope this clears things up!

[SammyWu11201]

I think I eliminated E because I mistakenly thought that "if tested by the antibody test" makes the necessary condition "anybody infected by virus X will for a time fail to exhibit infection." So I was thinking how is it even possible that the test makes for this necessary condition to happen. But now looking back, these two conditions can rather stand on its own, right? AC E just randomly linked these two conditions up, but on its own right, these are stand alone conditions?