Bows and arrows have _______ been out of use.　 

----You look tired, Jack. ----I feel quite rested, _______.

Two middle-aged passengers fell into the sea. ______, neither of them could swim.

--- What a lot of fun it is to play on a frozen sports field! --- Isn’t it rather risky,       ?

Make sure the gas is turned off after cooking, which would        cause danger to our life.