PrepTest 117, Section 1, Question 18

Working the answers

• A

  Excess cells and anti-NGF antibodies both appear, but no one says the excess cells produce those antibodies. This invents a mechanism linking two separate facts.

• B

  We aren't given this comparison of the number and qualities of cells grown with and without NGF. The fact that certain cell types need NGF doesn't establish the proposed comparison.

• C

  The account says embryos produce excess cells. It doesn't say few of the cells that actually connect with their targets are needed. That applies the excess-cell finding to a different group.

• D

  Nothing describes nerve cells being converted into another type of tissue.

• E
  Correct

  This takes more connecting than the other choices. Embryos produce more nerve cells than are ultimately required, and the surviving number adjusts to the tissue needing nerves. The final paragraph then links target tissue, local NGF, and survival. Together, these details support a picture in which some initial nerve cells never form a target connection and do not become part of the surviving network.

  The embryo connection comes from the earlier research; the final sentence alone doesn't spell out this entire inference. Nor do we need to assume that NGF affects every type of nerve cell. E is the best-supported conclusion across the account, while the alternatives add specific mechanisms or comparisons we weren't given.