The correct option is A a
The option that has an error, is the correct option.
Option A: The error lies in part (a) as 'writer' is a singular noun. When we say 'one of those', we are referring to one from a group of people: 'those few post-colonial writers'.
So, 'writer' is the error (the correct is 'writers': one of those few post-colonial writers).
Hence, option A is the correct option with the error.
The other parts (b) and (c) do not have any error in them. They are grammatically correct and are complete in meaning.
Hence options B and C are not the right answers.
Option D is incorrect because the sentence has an error (a).