问题
选择题
-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
答案
答案：D
题目分析：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。