宇宙中两个相距较近的星球可以看成双星，它们只在相互间的万有引力作用下，绕两球连线上的某一固定点做周期相同的匀速圆周运动．根据宇宙大爆炸理论，双星间的距离在不断缓慢增加，设双星仍做匀速圆周运动，则下列说法正确的是（   ）

在购买带装食品时，从食品安全的角度考虑，必须注意的有（　　）

①生产厂家　②生产日期　③食品价格　④保质期限　⑤储存方法．

阅读短文，从A，B，C，D四个选项中，选出可以填入空白处的最佳选项。

    What do you do after class at your school? You may say you go 1 and do 2 homework. But I think we can have 3 other things to do after class.

    We can 4 different clubs, like the art club and the music club. What can you do? If you swim well, you 5 in the swimming club. Maybe(也许) you can't play the violin 6 the guitar well, but you can 7 to play them at the music club. 8, some people there can help you. I like books and I often go to the 9 club. Do you like books? Come 10 me.