题目内容：

Safety comes first. Which is right?

① When you are alone at home, open the door as soon as someone knocks at the door.

②Pay attention to the gas, water and electricity.

③Walk across the street when the traffic lights turn green.

④Don’t mention our private matters when we meet a stranger.

⑤Always meet the persons who you know on the Internet.

A.②③④ B.①②⑤ C.①③⑤