问题补充:
I had been looking for the book for two days I found it at last.
Auntil
Bwhen
Cwhile
D. before
答案:
A. until
B. when
C. while
(答案→)D. before
解析:考查连词:A. until直到,B. when当…时候,C. while当…时候,虽然,然而,D. before在…前面,…才…,因为前面是过去完成式,所以是发生在过去的动作前的动作,句意:在我最后找到它之前,我已经找了这本书两天了。或是:我找了这本书两天才找到。选D。