题目

—What were you doing at 7:00 yesterday evening, Lisa? —I ________ up the kitchen with my mother. A． clean B． cleaned C． was cleaning D． am cleaning 答案：C【详解】 句意： ——昨天晚上 7 点你在干什么，丽莎？ —— 我和妈妈在一起打扫厨房。 考查动词时态。根据提问 “What were you doing at 7:00 yesterday evening”可知，询问的是过去某个时候正在做什么，应该用过去进行时 (was/were doing) ，这里主语为 I ，故选 C 。质子和电子分别以速度ν＝4．0×107m／s运动，试比较它们的物质波的波长．