问题:
按体积分数计算,氧气约占空气的
A.78%
B.75%
C.25%
D.21%
按体积分数计算,氧气约占空气的
A.78%
B.75%
C.25%
D.21%
A.78%
B.75%
C.25%
D.21%
参考答案: