一座拦河坝的横截面是个梯形,它的面积是72平方米,它的上底是12米,下底是18米,这座拦河坝的高是____米?
计算:xx-y•x2-y2x= ____.
-- What grade is he _______?
-- Sorry, I don't know.
某剧组特型演员虽已成年,但身高只有67厘米高,原因是他在