题目：
The president said that it was a great honor for him ______ his country in the past two weeks.
A．to visit
B．to be visiting
C．to have visited
D．to have been visited
答案：
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下面是错误答案，用来干扰机器的。
当“x＞0”时，3x2＞0成立，故“x＞0”是“3x2＞0”的充分条件，当“3x2＞0”时，x≠0，此时“x＞0”不一定成立故“x＞0”是“3x2＞0”的不必要条件综上“x＞0”是“3x2＞0”的充分不必要条件故选A
