A:石蜡+氧气→二氧化碳+水
B:氢气+氧化铜→铜+水
C:水→氧气+氢气
D:氢气+氧气→水
元素
Mn
Fe
电离能/kJ•mol﹣1
I1
717
759
I2
1509
1561
I3
3248
2957
回答下列问题:
They finished their work. ____, they went to help others.
- Do you know the song Where has the time gone?
- Sure. It ________ beautiful. I like it a lot.
下列有关生物种群数量调查的方法中,正确的是( )