Interactions with classmates and questions or topics posted by instructors are mostly found in ______.

The correct answer is discussion boards because they serve as a platform for students to engage in conversations about course material, share insights, and ask questions. Discussion boards are specifically designed for interaction, allowing classmates to post responses to questions or topics raised by instructors, fostering a collaborative learning environment.

In contrast, grades pertain to assessments and evaluations of student performance, course announcements are generally used for sharing important information about course logistics, and assignment submissions focus on delivering completed work to instructors. Each of these options serves distinct purposes that do not facilitate the same level of interaction among peers as discussion boards do.