将N2、CO、CO2的混合气体依次通入足量石灰水和灼热CuO后，冷却至室温，剩余

“四不放过”的内容是__________________、__________________、__________________、___________________。

设a＞b，则：

（1）2a（    ）2b；

（2）（x²+1）a（    ）（x²+1）b；

（3）3.5b+1（    ）3.5a+1。

燃油滤清器应采用（）清洗。

A、汽油

B、柴油

C、煤油

D、机油

His mother had talked to him for many minutes while he was watching TV,but ＿＿＿＿.

A．a little did he hear

B．little did he hear

C．little heard he

D．a little heard he

各类灭火器的代号是什么？