For one thing, he didn't trust his legs to hold him up.

首先，他不相信自己的腿能站起来。

Too cold, for one thing.

首先，太冷了。

Don't set him the task. For one thing he's old; for another he's in poor health.

不能让他去干，一则年纪大，二则身体弱。

Mastered by his better self he would have returned reluctantly up the tree, but for one thing.

如果不是因为他可以更好的掌握自己，他会不情愿地回到树上，但有一件事是肯定的。

For one thing, I firmly believe that reading can increase our knowledge. For another, reading helps us to calm down when we feel upset.

首先，我坚信阅读能增加我们的知识。另一方面，当我们感到沮丧时，阅读帮助我们平静下来。