题目

在极坐标系中，过点(2，)且与极轴平行的直线的方程是( ) A．ρcosθ＝                                             B．ρsinθ＝ C．ρ＝cosθ                                             D．ρ＝sinθ 答案：B [解析] 设P(ρ，θ)是所求直线上任意一点，则ρsinθ＝2sin，∴ρsinθ＝，故选B. －Did Jack come back early last night? －Yes．It was not yet eight o'clock ________ he arrived home． [　　] A．before B．when C．that D．until