Could and couldn’t

I couldn't (see) what was happening, so I had to change seats.

you open the window, please? It's really warm in here.

I couldn't (play) the guitar a year ago, but now I'm really good.

I can't run very fast now, but I when I was young.

I was unable to attend the meeting yesterday. you send me on the notes from it?

That be true - I've never seen him do anything like that before!

I speak in public when I first started work, but then I was trained to do it.

I couldn't attend the conference, but my colleague .

Could you (tell) me where the main reception is, please?

If you help me, I'd really appreciate it.