1 . ________ (如果没有重力), there would be no air around the earth. （根据汉语提示完成句子）

2 . ________the governments and scientists not worked together，AIDS－related deaths_______since their highest in 2005.
如果政府和科学家不共同努力，艾滋病相关的死亡就不会从2005年的最高点下降。

3 . ________ for the timely investment from the general public, our company would not be so thriving as it is.

A．Were it not

B．Had it not been

C．Be it not

D．Should it not be

4 . —What do you think of a house supplied by Lovell?
—         you buy a home from Lovell，the company promises to buy it back at the same price after three years.

A．Should	B．Must
C．Could	D．Would