12.Once he _______to do something ,no one can hold him back.
A.will make up his mind B.is making up his mind
C.made up his mind D.makes up his mind
句子是什么意思，为什么选D，不选其它。
27.The telephone ________ four times in the last hour , and each time it _________ for my roomate.
A.has rung;was B.was ringing ; is
C.had rung ; was D.rang;has been
为什么选C，不选A。
33.When I _______ , my granny ________.
A.was reading ; was falling asleep B.read ; fell asleep
C.was reading ; fell asleep D.read ; was falling asleep
为什么选C，不选D。
44.They told us that they ________ us to overcome any difficulties we would meet.
A.helped B.will help C.help D.were going to help
句子是什么意思，为什么选D，不选A。

1）意思：他一旦下定决心去做某件事，就没人能难得住他。因为can是现在时，所以用makes
2）last hour 说明是过去的事情所以用一般现在时，排除a，如果选a的话has和was时态就不一致了；因为电话铃响这个事已经发生并完成，所以用过去完成时，排除bd，
3）因为入睡是发生在读书这个过程之中的，所以用be reading ；对fall asleep来说睡着就睡着了，是瞬时发生的，不可能说正在睡着。所以不用d
4）因为would表明困难是将来的要遇到的，所以他们会帮助我们也自然是将来的是，所以用be gonging to 将要做，因为前面用told所以后面用were。意思是：他们告诉我们他们将会帮助我们战胜任何会遇到的困难