A:氧化镁与稀硫酸反应:MgO+2H+=Mg2++H2O
B:用醋酸除去水垢(主要成分CaCO3):CaCO3 + 2H+ = Ca2+ + H2O + CO2↑
C:利用腐蚀法制作印刷线路板:Fe3+ + Cu = Fe2+ + Cu2+
D:稀硫酸与氢氧化钡溶液反应:H+ + SO42- + Ba2+ + OH- = BaSO4↓ + H2O
They waited and waited for something _______ to happen.
如图,梯形ABCD中,AB∥CD,且AB⊥平面α,AB=2BC=2CD=4,点P为α内一动点,且∠APB=∠DPC,则P点的轨迹为( )
下列说法中正确的是( )