如图为嫦娥三号登月轨迹示意图.图中M点为环地球运动的近地点,N为环月球运动的近月点.a为环月运行的圆轨道,b为环月球运动的椭圆轨道,下列说法中正确的是( )
A:嫦娥三号在环地球轨道上的运行速度大于11.2km/s
B:嫦娥三号在M点进入地月转移轨道时应点火加速
C:设嫦娥三号在圆轨道a上经过N点时的加速度为a1,在椭圆轨道b上经过N点时的加速度为a2,则a1>a2
D:嫦娥三号在圆轨道a上的机械能小于在椭圆轨道b上的机械能
下列家庭垃圾中,适合用堆肥法处理的是( )
Hello,boys and girls! Nice to1 you! My name2 Alice Smith.I am a 3.I am a 13.Look, 4 this? It's a photo 5 my family.These are my parents and this is my6,Linda.She is 9.My mother is a teacher in a 7.My father is a teacher ,too.My pen is red.and Linda’s ruler is 8。too.Our 9 number is 826-9167.You can 10 us at it.I love my family.
若ab=|ab|,必有( )