Hi a.hopp!
Answer choice (A) is basically a restatement of the first sentence of the stimulus. The first two sentences convey the following conditional reasoning:
medieval European communities close-knit
respectful cooperation to meet basic needs close knit
The stimulus tells us that medieval European communities were close-knit. Mores specifically, it tells us that what made them close-knit was how they met basic needs--through respectful cooperation. To your question, this functions as a premise in the argument.
The argument then concludes by applying this principle to industrialized societies, suggesting that they too would become close-knit if they undertook more group tasks/respectful cooperation.