题目

— I should have gone to the wonderful concert with you yesterday. — _____. If possible, I wish I would have another such chance. A. Yes, you should      B. Take it easy C. What a shame         D. Don’t worry   答案：C表示遗憾，并希望下次有机会去。20．如图，在△ABC中，AB⊥BC，点D，E分别在AB，AC上，AD=2DB，AC=3EC，沿DE将△ADE翻折起来，使得点A到P的位置，满足$PB=\sqrt{3}BD$．（1）证明：DB⊥平面PBC；（2）若$PB=BC=\sqrt{3}，PC=\sqrt{6}$，点M在PC上，且，求三棱锥P-BEM的体积．