x→>XM 2x,dC=0 1( dx D(C)= M xdo 2t dC dc C=CM A 000 M 0 x M C1 C2 A1 B A C x C         d M d C = CM x → x M d 0 2 1 M =  C C x C         = − C C C x C C x t D C 1 d d d 2 1 ( ) M M