Yesterday morning I was just leaving the telephone rang.A. whenB. whileC. becauseD. since

问题补充：

Yesterday morning I was just leaving the telephone rang.

A. when

B. while

C. because

D. since

答案：

(答案→)A. when

B. while

C. because

D. since

解析：句意：昨天早上我正要离开时电话铃响了。When当…时；while当……时； because 因为；since自从。表示某事正在进行时发生了另一件事，常用when，所以选A。