The training session has been changed from 9:00 . . . . . . . . 10:00. A. at B. to C. in D. by

The correct answer is B. to.

The word “to” is used to indicate a change in time. In this case, the training session has been changed from 9:00 to 10:00.

The other options are not correct because:

• The word “at” is used to indicate a specific time. In this case, the training session is not being held at 9:00 or 10:00, it is being held between those two times.
• The word “in” is used to indicate a period of time. In this case, the training session is not being held for a specific period of time, it is being held between two specific times.
• The word “by” is used to indicate a deadline. In this case, the training session is not being held by a specific time, it is being held between two specific times.