划线部分不同的是（）

A．As a woman grows old, her beauty will gradually disappear.
B．A woman with a young mind never feels old.
C．Even a plainly dressed woman may have pure and real beauty.
D．However old she is, a woman with some excellent qualities can still maintain her beauty.

A．to show that city people all over the world have a lot in common
B．to let his readers be aware that they are some of the world’s biggest cities
C．to illustrate their difference from American cities
D．because they are some of the cities that attract visitors most