A:用超声波清除眼镜片上的垢迹
B:声波清洗精细的机械
C:医生用超声波为病人除去体内的结石
D:“B“超探病
—Well, it ______ a bit salty.
(Ⅰ)证明:PB∥平面AEC;
(Ⅱ)设二面角D﹣AE﹣C为60°,AP=1,AD= 3 ,求三棱锥E﹣ACD的体积.
—I won't get good grades_______ I study hard.
—That's ______ everyone is trying his best to prepare for the exam.