设z=z(x，y)由方程ez-xy2+x+z=0确定，求dz．
参考答案：令[*] 则 [*] 则[*] 则 [*]
A survey done recently show that not all parents _____ their children taking part in the weekend classes. [ ]
A. escape
B. lead to
C. imagine
D. approve of
根据不同的压力选择要使用的水带型号20、16、13、（）型。
A.10.0
B.8.0
C.1.0
D.2.0
