既是我国地势二、三级阶梯界线,又是农耕区与畜牧区界线的山脉是( )
A:贺兰山
B:长白山
C:巫山
D:大兴安岭
1).When did they do the survey? (last Thursday/last Friday)
2).What is the survey about? (breakfast/supper)
你可以这样开始:The students did a survey about…
Answer:____
一物体在光滑水平面上作匀速直线运动,现加上同一水平面内的一组共点力,能使物体移动一段距离后动能保持不变的是( )