Meaning of 'politeness costs nothing'

[Kawaii]

Test No. incompl/inter-14 "Popular Idioms (1)", question 9

Politeness costs ..........

(a) a lot
(b) a little
(c) much
(d) nothing

Test No. incompl/inter-14 "Popular Idioms (1)", answer 9

Politeness costs nothing.

Correct answer: (d) nothing
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Dear Torsten:
Can you explain me the meaning of this idiom? So simple but it is not easy to understand, thanks a lot.

Regards,

[Torsten]

Hi Kawaii,

Politeness costs nothing means that any person can be polite and friendly without having to pay money for it. Wouldn't you agree with that?
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Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary

[Velina]

Hi my name is Ivelina and I agree with that.