A
he started skating _at_ a very young age (age前用at）再如：
He died at the age of 89.(他89岁时去世）
D
The bus was very full,but the driver tired to _fit_ more people into it.(载更多人)
如：I want a bigger car,which can fit more people into it.
(想买个大点的车,那种可以装更多人的车.)