A number of tourists _________ Yangzhou many times because it is such a beautiful city.
Nowadays, more and more people would rather ____ __ in the country, because there is ______pollution there than in the city.
Dr. Ma is strict ______ local doctors and nurses, especially________their skills.
---When did you go to bed last night?---______________
It rained so_______ that people could _______ go out yesterday morning.
—I find the more we study, the more difficulty we have _______ out Maths problems.—Oh, I agree with you. Maths is more and more difficult.