What’s the matter with John? He has been sitting there for hours.—A postcard from his father _____ an attack of home-sickness in him.

The house, ______walls are red, is where my grandfather used to live ten years ago

So you didn’t say “hello” to him last night? —Well, I stopped and smiled when I saw him, but he me and walked on. [ ]

________ it is to visit theme parks in Beijing!

May I trouble you with the question—Sorry，but it is________my knowledge