BHA是什么意思？它有什么用途？

A. 10
B. 15
C. 20
D. 25

A. 正确
B. 错误

A. zero
B. equal to variation
C. eliminated by adjusting the compass
D. constant at any geographical locatio

A. 硫酸
B. 硝酸
C. 重氮
D. 盐酸