'the car on question' vs 'the car in question'

[Lio]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #653 "Prepositional Phrases - In, On, Out and Under (26)", question 6

Sir, the car ......... question was a late model green Toyota. I'll get the word out to the other officers to be watching for it.

(a) in
(b) on
(c) out
(d) under

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #653 "Prepositional Phrases - In, On, Out and Under (26)", answer 6

Sir, the car in question was a late model green Toyota. I'll get the word out to the other officers to be watching for it.

Correct answer: (a) in

Your answer was: incorrect
Sir, the car on question was a late model green Toyota. I'll get the word out to the other officers to be watching for it.
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why can't it be "on"

Lio

[Kitosdad]

"The car on question" makes no grammatical sense.
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