You can't imagine wahat great trouble they have____the problem ____A to solve ,being discussed B solving ;being talked aboutC to solve,to talk about D solving,to discuss

You can't imagine wahat great trouble they have____the problem ____
A to solve ,being discussed B solving ;being talked about
C to solve,to talk about D solving,to discuss

A
have to do sth
BD的ing形和have不能搭配
being discussed现在分词被动式做定语修饰problem,表示正在被讨论的问题

A

B
You can't imagine wahat great trouble (they have)____the problem( ____)
括号内为定语从句
have trouble (in) doing sth

B