What kind of sentence is it? This can be a complex subject, so don't compound the difficulty by skipping over the topic! It's simple, just have your class read and go over the information here and then complete the included exercise.

Click through links to learn how to write a business letter, a business email, and a friendly letter. Notes and sample letters for various types of letters are also available including complaint, interest, cover, apology, request,...

This informational site for teachers and students explains the importance of a letter of apology. Then the article articulates the types of information to include in friendly/personal apology letters and in formal/business apology letters.