. My first summer vocation in the high school, I spent a fortnight on the farm, is really unforgettable.
A. when
B. that
C. which
D. the one
网友回答
(答案→)A. when
B. that
C. which
D. the one
解析：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。