As far as we know, half of Canadian teenagers do not get enough sleep on school nights, _____?

—English has a large vocabulary, _______?—Yes. Know more words and expressions and you will find _______ easier to read and communicate.

Something has to be done to stop the rivers from being further polluted,       ?

—Excuse me, ________ is the library from here?—It’s about 5 minutes’ walk.

-- _________ will the foreign students be back from Nanjing?--In two days, I think.