Read each sentence to find out whether there is any grammatical error in it. The error if any will be in one part of the sentence, the letter of that part will be the answer. If there is No error, the answer is ( e ).i.e. 'No error'. (Ignore the errors of punctuation, if any.)
My frined lived at the top (a)/ of an old house (b)/ which attic had been (c)/ converted into a flat. (d)/ No error (e)

Answer

c

Explanation

Here, whose attic had been should be used. Whose is used to say which person or thing you mean.
Look at the sentence :
It is the house whose door is painted red.