Some of the sentences are grammatically correct and some are incorrect. Find out which part of the sentence has an error and mark that part. If there is no error , mark that part as your answer.
`("Travel agents around the world have come to rely on computers")/a` `("to book seats in air flights or room in hotels")/b` `("either today or a year from now")/c` `("No error")/d`

Explanation

(b) Use .on air flights.