____表示"当……时候"，既指时间点，又指一段时间，when 引导的时间状语从句中的动词可以是终止性的也可以是延续性的。

When the teacher came in, the students were talking.

When she arrives, I'll call you.

____表示"当……时候"，仅指一段时间，从句中的动作必须是延续性的，一般强调主从句的动作同时发生， while还可以作并列连词，意为"而、却"，表示对比关系。

Lisa was singing while her mother was playing the piano.

Tom is strong while his younger brother is week.

帝王谥号主要依靠其生前的行为而定。下列各项中，属于谥号的是（  ）

— How long have you been here?

—About half an hour, Jack ______me here.

在超市挑选有包装的食品时，与食品安全没有直接关系的是（ ）