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- Joined: Feb 02, 2011
- Fri Jan 21, 2011 12:00 am
#23737
Complete Question Explanation
Strengthen. The correct answer choice is (A)
The stimulus explains that whales must once have lived on land, because they have the remnants of a pelvis and a newly discovered whale skeleton has hind limbs and a partial pelvis.
The assumption is that appendages and structures had to serve a purpose at some time, so rudimentary structures normally used for walking tend to indicate a possibility that the animal evolved to walk.
The questions tells you to assume the stimulus is true, and to support the conclusion that the fragile hind limbs are the remnants of limbs that land-dwelling whales had.
Answer choice (A): This is the correct answer choice. If older fossils indicate that whales once had full pelvises, that does not establish that the whales once had limbs capable of land-travel; however, that does establish a trend that makes the argument's assumption work for it. The direction in time suggests that the whales walked at some time in the past, and are gradually loosing the structures needed for walking as, well, their legs are no longer so necessary.
Answer choice (B): If no whale skeletons with land-walking capable structures have been found, that cannot support the conclusion that whales once roamed the terrestrial realm. This choice is wrong.
Answer choice (C): If scientists are uncertain about what non-functioning limbs indicate about ancestral, functioning limbs, that does not help the conclusion that ancestral whales definitely had functioning limbs. This response is wrong.
Answer choice (D): This choice may have seemed attractive; however, you are supposed to help show that whales once had limbs that made them capable of walking on land. This choice helps show that a creature can be land-dwelling without fully functional limbs, which helps show that whales may have been land-dwelling, but not that they had functional limbs. This choice is incorrect.
Answer choice (E): Whether or not dolphins have no visible indication of hind limbs is irrelevant to whether whales themselves have such indications. This choice is wrong.
Strengthen. The correct answer choice is (A)
The stimulus explains that whales must once have lived on land, because they have the remnants of a pelvis and a newly discovered whale skeleton has hind limbs and a partial pelvis.
The assumption is that appendages and structures had to serve a purpose at some time, so rudimentary structures normally used for walking tend to indicate a possibility that the animal evolved to walk.
The questions tells you to assume the stimulus is true, and to support the conclusion that the fragile hind limbs are the remnants of limbs that land-dwelling whales had.
Answer choice (A): This is the correct answer choice. If older fossils indicate that whales once had full pelvises, that does not establish that the whales once had limbs capable of land-travel; however, that does establish a trend that makes the argument's assumption work for it. The direction in time suggests that the whales walked at some time in the past, and are gradually loosing the structures needed for walking as, well, their legs are no longer so necessary.
Answer choice (B): If no whale skeletons with land-walking capable structures have been found, that cannot support the conclusion that whales once roamed the terrestrial realm. This choice is wrong.
Answer choice (C): If scientists are uncertain about what non-functioning limbs indicate about ancestral, functioning limbs, that does not help the conclusion that ancestral whales definitely had functioning limbs. This response is wrong.
Answer choice (D): This choice may have seemed attractive; however, you are supposed to help show that whales once had limbs that made them capable of walking on land. This choice helps show that a creature can be land-dwelling without fully functional limbs, which helps show that whales may have been land-dwelling, but not that they had functional limbs. This choice is incorrect.
Answer choice (E): Whether or not dolphins have no visible indication of hind limbs is irrelevant to whether whales themselves have such indications. This choice is wrong.