“a=2”是“直线ax+2y=0平行于直线x+y=1”的　    [     ]

A．充分而不必要条件

B．必要而不充分条件　

C．充分必要条件

D．既不充分也不必要条件

Timmy was only 11 years old, but he is already 1.7 meters tall. He is too tall __________ his age, I think.

A．at

B．in

C．about

D．for