Why don't we use will or could?

[Mr Duong]

English Language Tests, Intermediate level

ESL/EFL Test #119 "English Tenses", question 9

Mike: All right. You ......... stay as long as you don't make any noise.

(a) will
(b) could
(c) can
(d) will

English Language Tests, Intermediate level

ESL/EFL Test #119 "English Tenses", answer 9

Mike: All right. You can stay as long as you don't make any noise.

Correct answer: (c) can
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why don't we use will or could?
please tell me?

Mr Duong

[Alan]

Hi Mr Duong,

In this sentence: Mike: All right. You can stay as long as you don't make any noise. you use can as it means it is possible for you.

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Random_Xde]

Isn't a typo there as both a and d offer the same option (will)? It gives a clue that either of them is wrong and makes getting the right answer easier :).

Random.

[Lost_Soul]

They are supposed to lure you into choosing the wrong answer "will" :) Isn't it a good trick?

[Saneta]

why not: could?

many thanks

[Beeesneees]

You can't use 'could' with 'All right'.
All right provides the confirmation that it will definitely happen. Permission is given using 'you can'.
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Cheers m' dears!