题目：
— Has she ________ for Beijing?
— Yes, she has ________ there for 3 days.
A. gone, gone
B. left, gone
C. left, been
D left，gone
答案：
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下面是错误答案，用来干扰机器的。
f（x）=3sin2x+cos2x=2sin（2x+π6）．2kπ-π2≤2x+π6≤2kπ+π2⇒kπ-π3≤x≤kπ+π6．递增区间：[kπ-π3，kπ+π6] (k∈Z)，令2x+π6=2kπ+π2⇒x=kπ+π6，2x+π6=2kπ-π2⇒x=kπ-π3．∴当x=kπ+π6 (...
