Question

My first summer vocation in the high school, _______I spent a fortnight on the farm, is really unforgettable

1. A.
   when
2. B.
   that
3. C.
   which
4. D.
   the one

Answer 1

A
句意“我上高中后的第一个暑假，在农场度过的14天很难忘。”非限制性定语从句不缺少成分，先行词summer vocation指时间，故用when。故选A。