级数x-x3+x5+…+（-1）nx2n+1+…（-1＜x＜1）的和函数为（）。
A.A
B.B
C.C
D.D
参考答案：B
— Another cup of tea?
— No, thanks. I _____ be off. Gina is waiting for me.
A. can
B. must
C. may
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