已知函数f(x)对一切x满足xf(x)+3x[f′(x)2=1-e-x,若f(x)在点x0(≠0)处有极值,则()。
A.A
B.B
C.C
D.D
参考答案:D
解析:
He is a model for us young people. We all _____ him very much. [ ]
A. look up to
B. look up
C. look at
D. look after
下列添括号错误的是( )
A.-x+5=-(x+5)
B.-7m-2n=-(7m+2n)
C.a2-3=+(a2-3)
D.2x-y=-(y-2x)