1. It's on the tip of my tongue...
就在我嘴边，什么来着......

2. Now, let me see.
让我想想。

3. How shall I put it?
我该怎么说呢？

4. What's the word for it...
这个怎么说来着......

5. I can't say for certain.
这个我还说不准。

6. Now where was I?
我说到哪儿了？