________(1)The apples give off a very sweet smell.________

(2)Our food supply gives out at last. _______

(3) He gave up teaching only two years ago.________

(4) The old teacher gave away all his books to    the school.__________

(5)Please give me back the book I lent you._______

(6)I'11 never give in to difficulty.________

(7)Somebody gave away the secret. __________

横式采样器取样，必须在口门（）再提升仪器。

A、通流时

B、敞开时

C、关闭后

D、关闭前