word possibility

Couldn't is the natural choice.

fivejedjonCouldn't is the natural choice.

Thanks. Is that because of 'looked', which is in the past?

Also, what about in these sentences, are both possible?

I have looked everywhere and 'couldn't or can't' find the answer
I have been looking everywhere and 'couldn't or can't' find the answer.

Nice job on wasting 5jj's time!



Don't do this again.

Aspara GusDon't do this again.

I'd already deleted one duplicate post. I didn't spot the other.

fivejedjon Aspara GusDon't do this again.I'd already deleted one duplicate post. I didn't spot the other.

I posted again because I did not get the answer I was looking for. I wanted to know the reason. Sorry for double posting. Would you please comment on my last post. Sorry again! I am trying hard to improve my skills.

I have looked/have been looking everywhere, but I can't find the answer.
I looked everywhere, but I couldn't find the answer.

Little GirlI have looked/have been looking everywhere, but I can't find the answer.I looked everywhere, but I couldn't find the answer.

Thanks a lot, LGirl. I think that 'didn't' would also work instead of 'can't and couldn't' in the above examples. But I would like your confirmation on that please.

It can only replace 'couldn't'.

Little GirlIt can only replace 'couldn't'.

I see. I think it is also possible with the present perfect form (have looked) since it is a reporting status of an action in the past, but not with the present perfect continuous (have been looking). Do you agree?

Sure. It's not always a good idea to mix tenses, though.