柴油机配气机构气门的功用是控制（）。
A、进排气道的开启和关闭
B、排气道的开启
C、排气道的开启和关闭
D、进气道的开启和关闭
参考答案：A
There are many kinds of birds in Australia,and over 140 species of snakes,many of
____are extremely dangerous.
A．them
B．which
C．what
D．those
合同中约定安全生产费按施工费的1.5%计取。有何错误？
