When some of the stamps are difficult to find, ______

A．Some stamps have a flower or animal on one side.
B．Along with a picture on one side, there are also some words.
C．Some used stamps can be worth a lot of money.
D．A stamp, when used, is worth more than a new on

A．When a child is two years old, he prefers to use both of his hands to grasp objects.
B．Scientists have given the reason for this tendency.
C．A monkey can use both of his hands equally well.
D．Those who prefer to use their left hands live a difficult lif