Difference between could and must?

[simone]

Test No. incompl/inter-73 "Modal Medley", question 10

......... you really help me? If so, I should be most grateful.

(a) Could
(b) Must
(c) May

Test No. incompl/inter-73 "Modal Medley", answer 10

Must you really help me? If so, I should be most grateful.

Correct answer: (b) Must

Your answer was: incorrect
May you really help me? If so, I should be most grateful.
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I do not understand why you use here must. for me with must sounds like an irony...
can u pls. explain.
thx,
Simone

[Torsten]

Hi Simone,

You are right - it should read could instead of must. Thanks for pointing out, we'll amend it.
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Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary