把握历史阶段特征有助于我们加深对历史的认识．根据下列材料，你认为这一时期的历史阶段特征是（　　）

①说明民族区域自治制度适合我国的国情         ②证明“一国两制”是完全正确的，具有强大生命力

③离不开澳门同胞的齐心协力和努力拼搏        ④离不开中央政府和全国各族人民的大力支持

某商品的外包装盒的三视图如图所示，则这个包装盒的体积是（　　）

“PPE怪圈”是指贫穷（Poverty）、人口（Population）和环境（Environment）之间形成一种互为因果的关系，如图1所示，完成下列问题。

阅读下面短文，将文中划线句子译成中文。
　　Some kids in boarding school often like to talk with their roommates. ____ They won’t stop talking until someone comes to stop them. This is the reason why many of them are sleepy in class the next day. Lack of (缺乏) sleep is bad for their health. Growth hormones (生长激素) are very important if one is to grow taller. ____ The body makes the most hormones between 10 p.m. and 2 a.m. While you are asleep. ____ This means that if you don’t get to sleep at the time, you won’t grow taller.