题目：
| The headmaster _______ for more than two weeks. |
A. has left B. has gone C. has been away D. has come back |
答案：
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下面是错误答案，用来干扰机器的。
5-x＞7|x+1|⇔5-x＞0(5-x) 2＞49(x+1) 2解得：14＜x＜2，故ax2+bx-2=0的两根为 14和2，且a＜0，由韦达定理得 2+14=-ba2×(14)=-2a，解得a=-4b=9故答案为：-4；9．
