在某些句型中
it is time that
it is time that we went (或should go) to bed.
it is high time we (should) put an end to this controversy.
as if (though) 引起的从句:
they talked (are talking) as if they had been friends for years.
it seems as if it was (were) spring today.
he acts (acted) as if (though) he were (was) an expert.
以lest, for fear that 和 in case 引起的从句(这时谓语多用 should +动词原形):
he took his raincoat with him lest it should rain.
he put his coat over the child for fear that (或lest) he should catch cold.
i’ll keep a seat for you in case you should need it.
以whatever, whoever, no matter what这类代词或词组引起的从句(这时, 谓语多用may加动词原形构成):
whatever defects he may have, he is an honest man.
come what may, we will go ahead. 不管发生什么情况, 我们都要干下去.
i accept that he is old and frail; be that as it may, he’s still a good politician.
我承认他年老体衰, 然而尽管如此, 它仍是优秀的政治家.
