Which is the valid identifier？（）

A. 3 / 2
B. 3 < 2
C. 3 * 4
D. 3 << 2
E. 3 * 22
F. 3 <<<2

A. The MyCircle class is full encapsulated.
B. The diameter of a given MyCircle is guaranteed to be twice its radius.
C. Lines 6 and 7 should be in a synchronized block to ensure encapsulation.
D. The radius of a MyCircle object can be set without affecting its diameter.