Correct option is C
Series:
ACETYLMETHYLCARBINOL,
YLMETHYLCARB,
ETYLMETHYLCARBIN,
METHYLCA,
YLMETHYLCARB,
?
Pattern:
Each term is a substring of the main word
"ACETYLMETHYLCARBINOL"
Observing carefully:
Parts are being picked and shortened progressively.
Following pattern → next term = THYL