Petrol is sold . . . . . . . . the liter.

A. by

B. on

C. at

D. from

Answer: Option A

Solution(By Examveda Team)

A preposition is a word which comes before a noun or a pronoun and establishes a relationship between the elements of a clause or words. 'By' is correct as it indicates an agent. The other options are wrong as from, at, and on indicate a source, a specific location, and a surface respectively.