A:熟习弹奏简捷
B:熟悉拂弄简捷
C:熟悉弹奏简洁
D:熟习拂弄简洁
Last summer I took a course on _______.
如图,在四棱锥P﹣ABCD中,PA⊥CD,AD∥BC,∠ADC=∠PAB=90°,BC=CD= 12 AD.