问题补充：
The problem is hard but Tom hasa good idea to solve it.
A. caught up
B. came up with
C. caught up with
D. comn up wlth
答案：
A. caught up
B. came up with
C. caught up with
(答案→)D. comn up wlth
解析：句意：这个问题很难，但是汤姆已经想出了解决他的主意。Come up with提出，想出catch up with超过，赶上，结合语境可知用现在完成时have done ， 故选D。
