Read the sentence below to find out whether there is any grammatical error in it. The error, if any, will be in one part of the sentence. Choose the option with that part as your answer. If there is no error, choose 'D' as your answer. (Ignore the errors of punctuation, if any).
Last month we celebrated the wedding of our sister for whom we have been looking for a suitable alliance for three years.
Last month we celebrated
the wedding of our sister for whom
we have been looking for a suitable alliance for three years.
No error.
Correct answer is C
we had been looking for a suitable alliance for three years.