r by accident or ___________,he arrivedtoo late to help us

It is uncertain ________ side effect the medicine will bring about, although about two thousand patients have taken it.(2010·浙江)

Last Sunday, I went shopping with my mother,_____ we bought many things.

Mr. Chen teaches __________math. We all like _________ very much.

Study hard ! _____you study, _____results you’ll get.