I shall call …… you tomorrow. A. at B. on C. with D. by

The correct answer is A. at.

The preposition “at” is used to indicate a specific time. In this case, the speaker is saying that they will call the listener at a specific time on the following day.

The other options are not as appropriate in this context. The preposition “on” is used to indicate a specific day or date. The preposition “with” is used to indicate a person or thing that is associated with something else. The preposition “by” is used to indicate a means or method of doing something.

Here are some examples of how the other options could be used:

• I will call you on Monday.
• I will call you with my new phone number.
• I will call you by phone.