题目

如f(x)=a0+a1x+a2x2+…+anxn,则令___________,得a0+a1+…+an=f(1),令__________,得a0-a1+…+(-1)nan=f(-1),a0+a2+a4…=,a1+a3+a5+…=;要得常数项,只要令____________即可.又如f(x,y)=a0xn+a1xn-1y+…+arxn-ryr+…+anyn,则f(1,1)=a0+a1+…+an;f(1,-1)=a0-a1+a2-…+(-1)nan等都可用特殊值方法求展开式中某些项的系数和. 答案：x=1 x=-1 x=0_____ he works hard, I don’t mind when he finishes the experiment. A. As soon as  B. As well as   C. So far as    D. So long as