问题补充:
My father walked in the room, looking as if he was thinking over something.
A. now and then
B. up and down
C. again and again
D. over and over
答案:
A. now and then
(答案→)B. up and down
C. again and again
D. over and over
解析:now and then表示时间;again and again和over and over表示次数。这三个短语都不符合语境。walk up and down in the room意思是“在房间里踱来踱去”。