I noticed that it is very difficult for Li Ming's uncle to raise him.

This math problem is difficult to work out.

I will let you know as soon as I arrive in Beijing.

He woke up very late, so he missed the plane to Beijing (in fact, you shouldn't use so that, because so that usually means intentionally).

6. Learning English grammar is not as difficult as learning spoken English.

He pretends to know me, but in fact he doesn't know me.

Although he worked hard, he failed.

What puzzles me most is how he can solve such a difficult math problem.

10. Our English teacher is very humorous, which is why his courses are very popular with his classmates.