英语：have trouble/problems/difficulty加动词ing还是to do还是done

一、句子的主语一般可以由→
1.名词【 Mr.Chen】 is a well-known scientist.
2.代词【He】 works very hard at school.
3.不定式【To go to a good university】 is his first goal.
4.动名词【 Doing morning exercise 】is good for your health.
5.从句【What she saw 】made her a little frightened.
二、要注意的是,动词不能充当句子的主语!如 Go to college is my dream,这句就错,应该改成To go to college.