计算

____ ____

如图所示，三个质点a、b、c质量分别为m₁、m₂、M，（M＞＞m₁，M＞＞m₂）．a、b在同一平面内绕c沿逆时针方向做匀速圆周运动，它们的周期之比T_a：T_b=1：k．（k＞1，为正整数）从图示位置开始，在b运动一周的过程中，则（   ）

读《别饿坏了那匹马》，根据课文内容，回答问题。

他家没有马，本不需要马草，残疾青年为什么还“认真地看了马草”？

根据短文内容判断下列句子正误。
    My name is Amy. Tomorrow is Saturday. My parents aren't going to work, but we are going to be very busy tomorrow. My mother is going to buy something. I'm going to the bookstore in the morning. Then I'm going to buy a dictionary.
    Tomorrow evening we are going to visit my grandparents and have a big dinner. After that we are going to the cinema. I think we are going to have a nice weekend.

如图，结合所学地理知识及“世界某半岛示意图”，回答问题。图中半岛地区河流众多，其具有的共同水文特征是（    ）