—______ is the ruler?       —______ two dollars.  

A．How much;It is

B．How much;They are

C．How many;They are

D．How many;It’s

二氧化碳气体保护焊时，电弧温度约为（）℃，电弧光辐射比手工电弧焊强，因此应加强防护。

A.3000-3300

B.5000-6000

C.6000-10000

D.10000-14000