Giúp mình câu 19, 20 với ạ.

19. I don't visit Van Mieu as often as Hoan Liem Lake. (les) .) 20. We will have to make him work harder. >He will 21. We breathe alot of polluted air; we get weaker. The more.... 22. If she had seen him waving, she would have waved back. >She didn't moisy but we enjoy living there. 07 ...