12.若(x+3y)2=(x-3y)2+M,则M为( )
0 283539 283547 283553 283557 283563 283565 283569 283575 283577 283583 283589 283593 283595 283599 283605 283607 283613 283617 283619 283623 283625 283629 283631 283633 283634 283635 283637 283638 283639 283641 283643 283647 283649 283653 283655 283659 283665 283667 283673 283677 283679 283683 283689 283695 283697 283703 283707 283709 283715 283719 283725 283733 366461
| A. | 6xy | B. | 12xy | C. | -6xy | D. | -12xy |