力所能及
in one's power
within one's power
do everything in one's power
as one's capacity allows
the best of one's power
the full extent of one's capability
例：
1.人只能做力所能及的事。
A man can do no more than he can.
2.这完全是你力所能及的工作。
This is a task well within your ability.
3.此事非你力所能及。
It's beyond your might.
