In Activity Center you select projects using checkboxes next to their names. Checking at least one project selection checkbox will immediately make the batch operation panel visible.
To allow for quick selection of activities or sub-activities under a project, you can use special menu available for projects with activities.
The menu is accessible via a downward arrow beneath the checkbox next to a project (with activities), which appears when the pointer is placed on the checkbox ().
Clicking the arrow opens a context-sensitive menu. When applied to projects it allows checking/unchecking all activities (shortcut: Click + Ctrl). When applied to activities, checking/unchecking all sub-activities is available.
Since the menu is context-sensitive, if a project has already all activities selected, the menu will contain only one command: Uncheck All Activities (Click + Ctrl).

Selection Checkbox Status Chart
Checkbox Status |
Projects |
Activities |
|
Unselected |
Unselected |
|
Selected for a batch operation, such as duplicating. |
Selected for a batch operation, such as duplicating. |
|
n/a |
The activity with sub-activities is selected as a single activity, without its sub-activities, for a batch operation, such as duplicating |
|
The project is not available for selection when some of its activities are selected for a batch operation, such as duplicating. |
The activity is not selected while some of its sub-activities are. Used when one or more of its sub-activities are selected for a batch operation, but the activity is not part of the batch. |