开始时活塞受力平衡,有:PASA=PBSB;假设气体体积不变,等容升温,有: PA TA = PB′ TB′ = △PA △TB ; PB TB = PB′ TB′ = △PB △TB ;故△PA= △T T PA,△PB= △T T PB;故△PASA=△PBSB,即活塞两边气体压力的增加量相同,活塞静止不动,但左侧气体压强增加量大,故AD正确,BC错误;故选:AD.