Polite vs. politeness

[clara]

Test No. incompl/elem-12 "We went on holiday", question 9

I believe it is ......... to hold a door open for a lady.

(a) politic
(b) polite
(c) political
(d) politeness

Test No. incompl/elem-12 "We went on holiday", answer 9

I believe it is polite to hold a door open for a lady.

Correct answer: (b) polite

Your answer was: incorrect
I believe it is politeness to hold a door open for a lady.
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why we used polite instead of politeness?

[Alan]

You need an adjective here: polite. It is correct (adjective) to answer the question with this word.
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