选取三枝同一植物的长势相同的枝条分别标记为A、B、C， 作如下表的处理后，分别插入相同大小的、盛有等量蒸馏水的量筒中，并以石蜡油覆盖密封水面，置于适宜环境条件下。2小时后观察记录各组量筒中蒸馏水的减少量（说明：涂抹凡士林能堵塞叶片相应部位气体进出的通道）。请回答下列问题：                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

枝条编号	枝条处理	蒸馏水减少量
A	不作任何处理	2mL
B	凡士林涂抹所有叶片下表面	0.5 mL
C	除去枝条上的所有叶片	0 mL