The best version is option C. Regular maintenance prolongs the life of your car. This is the only option that is grammatically correct.
Option A lacks the final '-s' in "prolong" that signals present simple tense and the third person. Option C, on the other hand, contains "prolongs" which is correctly conjugated.
Options B and D are incorrect because "maintenance" is an uncountable noun. That means that the noun cannot be in a plural form signalled by a final '-s' as in these sentences.
