辞职的时候该说点什么?

3. First of all, I'd like to say that I've really enjoyed working with you. However, I think it's about time for me to leave.
首先，我要说的是，我真的很高兴能和你一起共事。但是，我觉得该是我离开的时候了。

4.I've been trying, but I don't think I'm up to this job.
我一直很努力，但是我觉得自己无法胜任这个工作。