Supper ____________ ready.[ ]
A. am
B. is
C. are
答案:B
.函数f(x)=a4+5a2x2-x6的导数为
A.4a3+10ax2-x6
B.4a3+10a2x-6x5
C.10a2x-6x5
D.以上都不对
简述坡面水土保持林。