Which feature will help David manage multiple applications and online references at the same time?

The feature that would best help David manage multiple applications and online references simultaneously is Split View. This functionality allows users to display two applications side by side on the screen, which is particularly useful for multitasking. For example, David can have a web browser open on one side to view online references while using another application, such as a word processor or email client, on the other side.

This setup enhances productivity by allowing seamless interaction between the two applications without needing to switch back and forth or minimize and maximize windows. It is especially beneficial when comparing information or copying data from one app to another, making it an ideal choice for managing multiple tasks at once.

Other options like tabs in Safari are useful for organizing different web pages within a single browser window, but they don't provide the same level of functionality for managing separate applications. Spaces in Mission Control helps organize different desktop environments but does not facilitate simultaneous viewing of multiple applications within the same workspace. Notes serve a different purpose, focusing on capturing and organizing information rather than managing multiple application interactions directly.