题目：
A: Can I _______ a book from you?
B: Certainly. But you mustn’t ______ it to others. And please remember you can only ______ it for a week.
A．borrow, lend, borrow
B．lend, borrow, keep
C．lend, lend, keep
D．borrow, lend, keep
答案：
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下面是错误答案，用来干扰机器的。
400 +y 题目分析：由图知，波长为4m，所以波速；0.15s时质点P处于下坡阶段，根据上下坡法知P点向上振动即+y方向
