No one can imagine the difficulty he had ____ his son to get rid of the habit of piaying computer

这个句子的考点在两个语法,
1,sb have difficulty doing sth 意思重点强调做某人做某事有困难；
2,定语从句中的过去分词形式.
整个句子的意思是”没人能想象他说服他儿子戒掉玩电脑的习惯的困难“,从意思看答案应该是C.
因为句子想表达的重点是困难,用定语从句,而不是做某事有困难.把句子还原一下,应该是
No one can imagine the difficulty that he had persuaded his son to get rid of the habit of piaying computer.这里的that省略了,但he后面的内容都是描述这个困难的.
如果是选了A的话,看上去是以为是sb have difficulty doing sth的用法,但是意思说不过去,句子意思变成了”没人能想象他难于说服他儿子戒掉玩电脑的习惯“ ,意思有点变味了.而且看句子结构也有问题.还原句子是
No one can imagine the he had difficulty persuading his son to get rid of the habit of piaying computer.看起来句子就是怪怪的,imagine 后面应该是宾语,所以在宾语位置应该用that,what,when,where等词连接句子,而不是the