Question

In experiments ________ young teens are allowed to sleep as long as they want, they tend to sleep an average of 9 hours.

1. A.
   that
2. B.
   what
3. C.
   which
4. D.
   where

Answer 1

D
句意：在允许青少年想睡多久就睡多久的试验中，他们的（自然）睡眠时间往往是平均9个小时。本题考查定语从句，先行词为experiments，在定语从句中作状语，因此要用关系副词where。