电、气焊地点的风流中，瓦斯浓度有什么要求？
参考答案：
电、气焊地点的风流中，瓦斯浓度不得超过0.5％。
—Father's Day is coming. I'm going back home.to see my father.
—___________. [ ]
A. Give my best wishes to him
B. It's very kind of you
C. Say goodbye to him, please
D. See you soon
A．mgtgθ
B．mgsinθ
C．μmg
D．μmg
mgtgθ
mgsinθ