X
Y
Z
①
Cu
CuO
Cu(OH)2
②
CH3CH2OH
CH3CHO
CH2═CH2
③
Na2CO3
NaOH
NaHCO3
④
CaCO3
CaO
Ca(OH)2
我国水旱灾害比较频繁的主要原因是 ( )
Kangkang is __________ TV.