Course announcements that all students see, messaging, and chat fall under ______.

The correct choice highlights the role of course announcements, messaging, and chat as key tools for facilitating interaction and communication in an online learning environment. This is essential for keeping students informed about course updates, deadlines, and important information. Effective communication within an online course supports student engagement and can enhance their overall learning experience.

In contrast, course materials generally refer to the content and resources needed for the class, such as readings and assignments. Learning resources pertain to additional supportive materials that aid in understanding the primary course content. Calendar events are specific dates and times for certain deadlines or activities but do not encompass the broader scope of ongoing communication. Therefore, identifying the category of "communications" appropriately captures the interactive and informative aspects of the tools mentioned.