Read each sentence to find out whether there is any error in it. The error, if any, will be in one part of the sentence, the letter of the part is the answer. If there is No error, the answer is ( e ).
When he lent me (a)/ some money, he asked (b)/ to return it back (c)/ within a week. (d)/ No error (e)

Answer

c

Explanation

Use of back with return is supperfluous. 'He hardly knows to be used.