單項(xiàng)選擇題熔化極氣體保護(hù)焊（GMAW）時(shí)，保護(hù)效果更好的是以下哪種成份的氣體？（）
A.Ar=99.5% H2O=0.1%
B.Ar=99.5% H2O=0.2%
C.Ar=99.8% H2O=0.1%
D.Ar=99.8% H2O=0.15%
A.Ar=99.5% H2O=0.1%
B.Ar=99.5% H2O=0.2%
C.Ar=99.8% H2O=0.1%
D.Ar=99.8% H2O=0.15%
