Which two statements are true about mouse button variables?（）
A. SYSTEMOUSE_BUTTON_PRESSED returns a string.
B. SYSTEMOUSE_BUTTON_PRESSED returns a numeric value. 1Z0-132 World Leaders In Certifications Material - Test-king.com
C. A possible value for SYSTEMOUSE_BUTTON_MODIFIERS is Control+Alt+Delete.
D. SYSTEMOUSE_BUTTON_MODIFIERS can only be references in form-level triggers.
E. SYSTEMOUSE_BUTTON_MODIFIERS identifies which special key was pressed in conjunction with the usual mouse button action.&e
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