Question

Fill in the blank with a suitable preposition.

He promised to return _____ an hour, but he didn't.

• A. within
• B. by
• C. in
  
• D. of

Answer 1

Answer: (A), (C)

in
within

'Within' is used to indicate that the event will occur before the end of the time given (example, before the 60 minutes is over).

'By' is used to indicate that the event may occur anytime in the given range.
'In' is used to indicate that the event will definitely occur in the given time period.
'Of' is incorrect in the given context.

So, the possible answers are options C) In and A) Within.