you _____pay for the book if you _____it

A don't need to ;needn't B don't need ;don't need C needn't ;needn't D needn't ;don't need

D
如果你不需要这本书，你没必须付钱

前一个是没必要，用needn't
后一个是不需要，所以用don't need

~~~~~~~~~~～～~~~~祝你进步，如对你有帮助，请及时采纳~~~~~~~~~~~~~~~~

D，前一个空做情态动词表示不需要，后一个就是普通的动词

我觉得选A 如果你不需要这本书 你没必要付钱

1.if you lost a book,you had to pay for it lost 是过去式，所以用 had 2.the ship would have sunk if it was not for the 如果不是船长，船会沉的，过去的假设，所以用 was 3.they should have studied but they wasted so much precious time 他们应该学习的，但却浪费了太多的宝贵时间 后边过去式wasted ，前边用 完成时 4.if i had time tomorrow ,i would come to help you 前面一般时态假设，用过去式had，后面would后接一般现在时！ 希望帮到你，谢谢~

这句话首先要确定的是主将从现，主句用将来时，从句用一般现在时表示将来。因此第二个空要填need做实意动词的用法，做实意动词的否定时，要有相应的助动词+not.因此排除A，C. 主将从现的句子，主句除了可以用将来时，还可以用情态动词+原形动词。因此选D