Meaning of 'no problem'

[Guest]

Test No. incompl/elem-33 "Responses (6)", question 1

John: 'Thank you so much.'
Sue: '.........'

(a) No problem.
(b) Any problem.
(c) A problem.
(d) Some problem.

Test No. incompl/elem-33 "Responses (6)", answer 1

John: 'Thank you so much.'
Sue: 'No problem.'

Correct answer: (a) No problem.
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how much is it?

[Alan]

This means it's all right.
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English as a Second Language
You can read my ESL story A day in the life of a driving instructor