A:赤道附近
B:森林覆盖良好的水库区
C:东海海域
D:沙漠地区
我国水土流失最为严重的地区是( )
Our Chinese teacher recommends new book to us every month and asks us to read by ourselves after school.
某放射性元素质量为M,测得每分钟放出1.2×104个β粒子,21天后再测,发现每分钟放出1.5×103个β粒子,该放射性元素的半衰期是多少?
选项
甲
乙
丙
A
H2SO4
H2
H2O
B
C
CO
CO2
Ca(OH)2
CaCl2
CaCO3
D
NaOH
NaCl
NaNO3