The Ras protein functions as a molecular switch that is set to its onstate by a guanine-nucleotide exchange factor (GEF) that causes it to bind GTP. A GTPase-activating protein (GAP) resets the switch to the off state by inducing Ras to hydrolyze its bound GTP to GDP much more rapidly than in the absence of the GAP. Thus Ras works like a light switch that one person turns on and another turns off. In a cell line that lacks the Ras-specific GAP, what abnormalities would you expect to find in the way Ras activity responds to extracellular signals

蒸汽采暖系统根据立管的数量分类，包括（）。

A．干式回水采暖系统

B．湿式回水采暖系统

C．单管蒸汽采暖系统

D．双管蒸汽采暖系统