A．The melting Arctic ice has drowned many coastal cities．
B．Arctic ice is a major source of the world’s flesh water．
C．Arctic ice is essential to human survival．
D．The decline of Arctic ice is irreversible．

A．There is no easy technological solution to it．
B．It will advance nuclear technology．
C．There is no easy way．to understand it．
D．It will do a lot of harm to mankind．

A．The deciding factor in children’s academic performance．
B．The health problems of children raised by a single parent．
C．The relation between children’s self-control and their future success．
D．The reason why New Zealand children seem to have better self-control．