Question

I couldn't have got to the meeting on time - _______ an earlier train .

A．if I had not caught

B．unless I had caught

C．if I did not catch

D．unless I caught

Answer 1

B

if…not和unless有時(shí)可以互相替換，但也有不能互相替換的時(shí)候。unless用于這樣的句子，即"如果A不受阻于B，A將發(fā)生"，例如：He will accept the job if the salary is not too low / unless the salary is too low . (如果薪水不太低，他就會(huì)接受這一工作/除非薪水太低，否則他會(huì)接受這一項(xiàng)工作的。)但是unless不能用于"由于未發(fā)生B而發(fā)生A"的句子里，如：I will be quite glad if she does not come this evening (她今天晚上要是不來，我才高興呢。)又如：I will be surprised if he does not win the game next week . (如果他贏不了下星期那場(chǎng)比賽，我倒會(huì)感到驚奇的。)在以上的兩個(gè)句子中不能使用unless，但是unless常用來引導(dǎo)一個(gè)談及過去的事后的想法，unless從句跟著主句，通常用破折號(hào)而不是逗號(hào)將它與主句分開。第7題的句意是：我不可能準(zhǔn)時(shí)到會(huì)了-除非我當(dāng)時(shí)趕上更早一列火車。這個(gè)句子的實(shí)際是說：我沒有準(zhǔn)時(shí)到會(huì)。我只有趕上更早的一趟火車，才能準(zhǔn)時(shí)到會(huì)。如果用if … not代替上面句中的unless，那么這個(gè)句子就變成：I couldn't have got to the meeting on time if I hadn't caught an earlier train . (要不是我趕上了更早的一班火車，我就不可能準(zhǔn)時(shí)到會(huì)。)這句話表達(dá)的意思與上句完全相反：我確實(shí)準(zhǔn)時(shí)到會(huì)了，因?yàn)槲亿s上了更早的一趟火車。