she will sing a song____she is asked.A.if B.unless C.for D.since 请问选哪一个 为什么呢? 谢谢
问题描述：
she will sing a song____she is asked.
A.if B.unless C.for D.since 请问选哪一个 为什么呢? 谢谢
答
if
原因不太好说,语感是if
unless
应该这样说：she wouldn't sing a song ,unless she were asked.
for since
应该这样说：she sung a song,for/since she had been asked.