---Why were you late for school today?
----It was I help catch a thief on the bus.
A. since
B. as
C. for
D. because
网友回答
A. since
B. as
C. for
(答案→)D. because
解析：连词辨析。Since表示众所周知的原因；as由于；for表示补充说明，一般放在句末；because用来回答why的问句。句意：—为什么你今天上学迟到？—就是因为我帮助在车上抓了一个贼。故D正确。