Question

I coutdn't have got to the meeting on time____________ an earlier train.

A．if I had not caught	B．unless I had caugh
C．if ! did not catch	D．unless I caugh

Answer 1

B

if．．．not和unless有時也不能互相替換。unless不能用于“由于未發(fā)生B而發(fā)生A”的句子里，如：1 will be quite斟ad if she does not come this evening。unless常用來引導(dǎo)一個談及過去的事后的想法，unless從句跟著主句，通常用破折號而不是逗號將它與主句分開。