In my younger days a I could run four miles b at a stretch c No error d ........

English Aptitude (NDA) Error correction

SPOTTING ERRORS
Directions: Each item in this section has a sentence with three underlined parts labelled (a), (b) and (c). Read each sentence to find out whether there is any error in any underlined part and indicate your response in the Answer Sheet against the corresponding letter i.e., (a) or (b) or (c). If you find no error, your response should be indicated as (d).

In my younger days(a)/ I could run four miles (b)/at a stretch(c)./ No error (d)