宇宙中的有些恒星可组成双星系统。它们之间的万有引力比其它恒星对它们的万有引力大得多,因此在研究双星的运动时,可以忽略其它星球对它们的作用。已知S1和S2构成一个双星,它们在相互之间的万有引力作用下绕两者连线上某一定点O做匀速圆周运动。S1的质量是S2质量的k倍(k>1),下列判断正确的是
Our classes are over noon and then we go to have a rest 1:00 in the afternoon.( )
at; at
in; in
in; at
at; in
Many foreigners came to our school last week, including three and four .( )
German, American
Germans. American
Germans. Americans
German, Americans
boy in a black hat is my brother. He often plays chess with my friends.( )
A; the
The; /
The; a
A; /
Can I swim in the river?
No way. Look at the sign. It says No Swimming.( )
It's possible.
No door.
It's impossible.
No problem.
Why don't you play basketball with us?
That's not my cup of tea. I like reading at home better.( )
It's good for me.
I don' t want to drink tea.
It's my favorite.
It's not my favorite.