【单选题】纯交换经济中,两个人的无差异曲线的切点组成的曲线是( )。
【判断题】第一心音标志心室收缩开始,心室收缩力增强则第一心音加强。
【单选题】It was in the small house was built with stones by his father he spent his childhood.
【单选题】It was in the small house was destroyed by the flood he spent his childhood.
【简答题】直线y=2x-6与x轴交点坐标为______.
【单选题】It was in the small house ___ was built with stones by his father ___he spent his childhood .
【简答题】直线y=3x-6与x轴的交点坐标为______.