[辨与析] during,when,while
during后面接名词：I went to visit the Great Wall during the summer vacation.我暑假里去游览了长城.
when,while都意为“当…”,都引导时间状语从句.
when强调时间点,通常译为“当…”,例如：
When she came in,I was cooking.她进来时,我正在做饭.
while强调时间段,通常译为“正当……”,例如：
While he was cooking,a friend of his came to see him.当他正在做饭的时候,一个朋友来拜访他.