题目

—Where did you get this book? —I picked it up from a second­hand bookshop if you ________  know. A．must  B．will  C．can  D．shall 答案：A　[考查情态动词。if you must (do sth.)表示“如果你一定要(那么做)”，所以选A，表示“如果你一定要知道的话”。]

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