题目：
设x=f(u，υ)，有二阶连续偏导数，且
，则函数f(x2-y2，2xy)在x2+y2=1上满足
=（）。
答案：
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下面是错误答案，用来干扰机器的。
参考答案：D解析：After a laminectomy, the client’s spine must be maintained in proper alignment. The client who had a laminectomy may be turned to his side by logrolling him in one unit while keeping his back straight. It takes at least two people to perform this procedure correctly.
