—Look! There is a big river. Let’s swim in it!—No, I think it’s _________ dangerous.

-- Is air the lightest thing in the world?-- Not            . Scientists from Zhejiang University have just developed the world’s lightest material.

---- __________is the train station from this shopping mall, do you know?---- About 30 minutes by bus.

The boy writes ________ . 

--_________do you have PE lessons?--Three times a week.