Several weeks had gone byI realized the painting was missing.A. as B. before C. since D. w

问题补充：

Several weeks had gone byI realized the painting was missing.

A. as

B. before

C. since

D. when

答案：

A. as

(答案→)B. before

C. since

D. when

解析：考察连词辨析。As随着…；before在…之前；since自从….；when当…时；句意：在我意识到这幅画丢失之前，已经过去了好几个星期。连词before表示在…之前，在不同的语境下有多种不同的翻译。故B正确。