题目

已知P为△ABC所在平面外一点，PA⊥PB，PB⊥PC，PC⊥PA，PH⊥平面 ABC，则H为△ABC的(    ) A．重心 B．垂心 C．外心 D．内心 答案：BHaier Company produced a new type of refrigerator of high quality and pretty appearance; its only ___is that it takes up too much room. A. advantage        B. drawback          C. profit              D. mistake