​You have been asked to give an explanation for not attending an important official meeting. Your immediate boss who has not informed you about the meeting is now putting pressure on you not to place an allegation against him/her. You would​

Send a written reply explaining the fact.
This is a good professional approach. It allows you to calmly and clearly explain the situation, taking responsibility for what is within your control, and avoids direct confrontation. It also provides a record of your explanation.​​

Thus, the correct option (c).