如图所示,在发射地球同步卫星的过程中,卫星首先进入椭圆轨道I,然后在Q点通过改变卫星速度,让卫星进入地球同步轨道Ⅱ,则( )
A:该卫星的发射速度必定小于11.2 km/s
B:卫星在轨道上运行不受重力
C:在轨道I上,卫星在P点的速度大于在Q点的速度
D:卫星在Q点通过加速实现由轨道I进入轨道Ⅱ
在Rt△ABC中,∠C=90°,sinB= 22 ,则∠A的度数为( )
下列有关分子、原子、离子的说法错误的是( )①分子、原子、离子都是构成物质的粒子。②只有分子、原子可以保持物质的化学性质。③原子、离子都是由质子、中子和电子构成的。④离子也可以得失电子变成原子。⑤原子是化学变化中的最小粒子,所以原子肯定不能再分。⑥化学变化的实质:分子破裂成原子,原子重新组合成新分子。⑦原子的种类由质子数或核电荷数决定。 ⑧原子的质量主要集中在原子核上
A
Linda,14
My mother does most of the housework like cooking and folding the clothes.My father can only do the washing,sweep the floor and take out the rubbish.He really needs to learn how to do the housework.
Celina,13
My mother and my father do 50% of the housework each.My mother does the washing and cleans the living room.My father makes the bed and drives me to school.
Paul,16
My father doesn't do a lot but he tries to help.He hangs__up the clothes after my mother washes them and my mother is happy that he always gives her a hand.
Bill,15
My mother is a doctor.She is busy with her work every day,so she has little time to do the housework.In fact,she isn't good at doing it.So my father has to do most of it.Sometimes my grandmother comes to help.