（ ）16.It is known to all that_____you exercise regularly，you won’t keep good health.

A.Unless

B.whenever

C.although

D.if

16.A【解析】unless“除非，如果不”；whenever“无论何时”；although“虽然，尽管”；if“如果，假如”。句意：众所周知，如果你不经常锻炼，你就不会保持健康。故选A。

（ ）17.My brother would like to buy a good watch but_____was available from that shop.

A.Nothing

B.none

C.no one

D.neither

17.B【解析】句意：我的哥哥想买一个好表，但是那个商店里没有合适的。none表示所有的都不，既可指人，也可以指物；no one相当于no body，只能指人。故选B。

（ ）18.He can’t remember when_____turning point occurred exactly，but it might be_____morning during his vacation.

A./；a

B.a；a

C.the；a

D.a；the