1. to the best of one’s ability中的ability可以用复数吗？

答：ability 用单数或复数都可以（但用复数不如用单数普通）。以下是摘自柯林斯词典的解释和例句：

If you do something to the best of your abilities or to the best of your ability, you do it as well as you can.

I take care of them to the best of my abilities. 我尽我所能地照顾他们。

They tackled them to the best of their ability. 他们竭尽全力给予解决。

2. 若表示“竭尽全力做某事”，后面是接不定式还是in doing sth, on doing sth之类的？

答：对于to the best of one’s ability 的使用，我们通常既不用 to the best of one’s ability to do sth，也不用to the best of one’s ability in / on doing sth 等，它通常所用的结构是 do sth to the best of one’s ability，这里的 to the best of one’s ability 起强调作用（指“到能力的极限”，也就是“尽力”“竭尽全力”的意思），你自己摘录的句子已充分说明了这一点。再补充几例句，你注意体会：

Just do the work to the best of your ability. 只要你尽力做就行了。

We will keep you informed to the best of our ability. 我们将竭尽全力为您提供最新信息。

I will carry out your instructions to the best of my ability. 我将尽全力执行你的指示。

I promise to carry out my duties to the best of my ability. 我许诺就自己能力所及履行我的职责。

Every game, we go out and play to the best of our ability. 我们每场比赛都倾尽全力地去拼。

We must exploit what we have to the best of our ability. 我们必须尽量利用我们拥有的一切。