Which statement is true about mouse events? （）

• A、The cursor style can be set to CAUTION. 
• B、Double-clicking a mouse button can potentially fire six mouse event triggers. 
• C、The values for the SYSTEM.MOUSE_BUTTON_PRESSED system variable can only be 1 or 2. 
• D、Click and double-click button actions can only detect if the mouse is positioned in an item.