The most suitable is a quiet exam (6)
I believe the answer is:
aptest
'the most suitable' is the definition.
(I've seen this before)
'a quiet exam' is the wordplay.
'a quiet' becomes 'ap' (I've seen this in other clues).
'exam' becomes 'test' (synonyms).
'ap'+'test'='APTEST'
'is' is the link.
(Other definitions for aptest that I've seen before include "most seemly" , "Most suitable" , "very fit" .)