─             did they go to work last week ?     ─Once .

I don’t know if Mr Green ________. If he ______, I will let you know.

 --Let’s go shopping, _____? --Ok, let’s go.

 —President Obama has never been to Beijing, ______ he? — He visited the Great Wall on the afternoon of November 18th,2011.

-- Peter didn’t use to be heavy, did he?-- ________. But look, how thin he is!