23. Each member country of WTO must ______ its laws and regulations and compete on the principle of fairness and co-operation.

A．cater to

B．correspond to

C．relate to

D．submit to

低碳钢焊接时，对焊接电源没有特殊要求，可采用交、直流弧焊机进行全位置焊接，工艺简单。