I don't think you will have any difficulty( )his English speechA to understand B understand C in understanding 为什么选C

I don't think you will have any difficulty( )his English speechA to understand B understand C in understanding 为什么选C
I don't think you will have any difficulty( )his English speech
A to understand B understand C in understanding 为什么选C

I don't think you will have any difficulty( )his English speechA to understand B understand C in understanding 为什么选C
have difficulty (in) doing sth.在做某事方面有困难,in可以省略
因此选C

have difficulty in doing sth

have difficulty in doing sth
固定搭配，做……有困难

have some difficulty （in） doing sth.为固定搭配。
虽然 think 引导的宾语从句否定前置、提前至主句，
但句中some 在否定句仍需改为any, 固定结构就变成：
have any difficulty （in） doing sth. 固定结构的其后仍需跟V+ING，
因此，选C

have difficulty (in) doing sth. 在做某事方面有困难，in可以省略
固定搭配