题目内容
-This problem is very difficult. -I know,but Jack has working it out.
| A．succeed in | B．succeeds in | C．succeeding in | D．succeeded in |
D
解析试题分析：句意：这道题非常难。——我知道，但是杰克已经成功的计算出它来了。结合语境可知本句描述的是现在已经完成的动作，故用现在完成时态。选Ｄ。
考点：考查时态
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