. . . . . . . is a very regular class, sir.

The correct answer is: Option C: Your.

Explanation:

The sentence addresses someone directly with "sir," which indicates that the speaker is talking about the class belonging to the person they are speaking to.

"Your" is the correct possessive adjective that shows ownership by the listener. The complete thought is: "Your class is very regular, sir," which means the class that belongs to you is very regular.

Why not the other options?

"My" indicates the speaker’s own class, not the class of the person addressed as "sir."

"Mines" is grammatically incorrect; the correct form is "mine," which cannot come directly before a noun.

"Ours" is a possessive pronoun that stands alone and refers to shared ownership, but it cannot modify a noun directly (you cannot say "ours class"), and it doesn’t match the context of addressing someone formally as "sir."

Therefore, "Your" is the only option that fits both the grammar and context of addressing "sir."