第四，我选择了一本书作为主要课本，但它并不能真正帮助我解决碰到的问题。
Fourth, the book I selected as the primary text didn't really help solve the problems I encountered.
租书的价格十分合理，运书方式和租期也可以自由选择，而且，归还课本时寄送是免费的。
Prices are refreshingly reasonable; shipping options and rental periods are flexible; and return shipping is free.
由于教学时间很短，我不能教课本所有内容，需要选择一些经典的部分来教。
Because the teaching time was very short, I cannot teach all the section of the textbook, I have to choose some classic sections to tell.
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