I've [been sleeping] [slept] all day, and that is why I [could not] [haven't been able to] answer your calls.

[Marika33]

Which is best out of these?

1. I've been sleeping all day, and that is why I could not answer your calls. Sorry.
2. I've slept all day, and that is why I could not answer your calls. Sorry.

3. I've been sleeping all day, and that is why I haven't been able to answer your calls. Sorry.
4. I've slept all day, and that is why I haven't been able to answer your calls. Sorry.

 

[emsr2d2]

Use 1 or 3.

 

[Tarheel]

Perhaps: "Sorry for responding late. I've been napping."

 

[emsr2d2]

@Tarheel Sleeping all day is a bit more than napping!

 

[Tarheel]

@emsr2d2 True, but I would probably say it that way. Why? For one thing, I would probably figure they don't need to know more. Maybe I have something I want to talk about more, and I don't want to waste time on an explanation.

Dang! That was too much typing.

 

[emsr2d2]

In natural BrE, most of us wouldn't use the verb "sleep" at all. We'd use the adjective "asleep".

I've been asleep all day so I missed your calls.