the type of problems questions exams So they're optional, but they're very, very, very highly encouraged that you do these, because this is going to give you practice for the types of problems that are going to be on the exam.虽然它们是选做的，但是它们非常非常，非常值得你们去做，因为这对你们来说是一次训练,是用来熟悉考试题型的。The exams will be multiple choice and short answer, fill in the blank, that sort of thing.题型分为单项选择,简答,还有填空之类的
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