(1) Please be quiet. I ___ the speaker very well.
a.can't hear b.am not hearing c.couldn't hear
The answer is "a"， but I've a question ，if the sentences are
shown in a story or a past state, I could use "c",couldn't I?
(2) ___ help me carry this box?
a.Would you b.Do you c.Could you d.Let's
The answers are "a" & "c",
but I think "b" is also right, isn't it?!

(1) feels like a sentence out from a conversatio-n rather than narration. Sure, one usually usepast sentences in story narration, but that'd beweird or really rare case if it's conversation.(2) No. The question is about if you understandhow to request/ask for help in English, imo. And"Do you -" isn't used in that kind of situation.Do you eat breakfast every morning?Do you know who's the one behind you?

Thanks!!