What kind of variable should be used for a reusable Google Analytics property ID variable?

A User-defined Constant variable is the correct choice for a reusable Google Analytics property ID because it stores a fixed value that does not change. This ensures consistency across all tags that use it, preventing errors and simplifying management. You define the GA property ID once, and then reference this variable in all your Google Analytics tags. A User-defined Data Layer variable is incorrect because it retrieves values from the data layer, which are dynamic and can change based on user interaction or page content. A Built-in Event variable is incorrect as it captures specific event names, not fixed IDs. A Built-in Click Classes variable is also incorrect as it retrieves CSS class names from clicked elements, which is irrelevant for a GA property ID.