You look really cool in the new dress, dear. How much did you ________ it?
Can you learn English ________ chatting on the Internet?
He thinks _____ history about Chinese is very important.
How many states _______ the United States? Fifty.
My mother is strict both _____ me and ____ her work.
------ Do you know where Li Ming is working _____? ------ Maybe in Guangzhou, I think.