Statement A: During favourable conditins, the individual cells of slime moulds unite and form a multinucleate structure plasmodium.

Statement B: In unfavourable conditions the plasmodium differentiates into fruiting body. 

In cellular slime moulds, in favourble conditions, the uninucleate cells fuse and form a multicucleate syncytium called plasmodium (actually pseudoplasmodium). In unfavourable conditions, this plasmodium differentiates and forms fruiting body which forms spores with cellulosic cell walls dispersed by wind.