阅读下面短文，从每小题所给的A、B、C、D四个选项中选出最佳选项。

    How many calories (卡路里) are there in every meal you eat? That seems like a difficult question to answer. But students at Aitkin High School in the United States can easily answer it now. They put what they eat into an online calorie counter (计算器). It quickly tells how many calories there are in their meals.

In fact, this is part of the school's health class. It is about heart health, nutrition (营养), and fitness. Students can learn basic knowledge about fats, proteins (蛋白质), calories and sugar. Students can also learn how to balance calories in and out. They will know what happens when the balance isn't there. "The online calorie counter can help you make healthy choices. Making one healthy eating decision can really make a difference," Adam Carlson, the teacher of the class, told local newspaper Aitkin Independent Age.

They also talk about good ways to burn calories in the gym. According to Carlson, the gym is a great place to burn calories and get stronger. But it doesn't work for everyone. So they try to find different ways to exercise. "I'm trying hard to teach the students that doing exercise can be fun but hard, and doesn't need to take hours out of the day, but you should keep on doing it for a long time," she said.

    The class has changed students. "I am now watching what I am eating and pay attention to the food labels (标签)," said seventh-grader Karena Burgstaler. Another student James Erickson began to pay attention to how much sugar he eats because it was almost over his daily calorie intake goal.

有下列五种物质：①2﹣甲基丁烷；②2，2﹣二甲基丙烷；③戊烷；④丙烷；⑤丁烷．它们的沸点由高到低的顺序正确的是（　　）

阅读下列材料，然后从A、B、C、D四个选项中选出能回答所提问题或完成所给句子的最佳选项。

One night, when I was eight, my mother gently asked me a question I would never forget. “Cindy, my company wants to promote (升职) me but needs me to work in Brazil. This is like your teacher telling you that you've done well and allowing you to skip (跳) a grade, but you'll have to leave your friends. Would you say yes to your teacher?” She gave me a hug and asked me to think about it. I was lost in thought. The question kept me wondering for the rest of the night. I had said “yes” but for the first time, I realized the difficult decisions adults had to make.

     For almost four years, my mother would call us from Brazil every day. Every evening I'd eagerly wait for the phone to ring and then tell her everything happened during the day. A phone call, however, could never take her place and it was difficult not to feel lonely at times.

During my fourth-grade Christmas break, we flew to Rio to visit her. Looking at her large empty apartment,   ▲  It was then I started to understand the difficult choices she had to make. She needed to think about both family and work. Faced with difficult decisions, she used to tell me, you wouldn't know whether you make the right choice, but you could always make the best out of the situation, with a positive attitude.

     Back home, I reminded myself that what my mother could do, I could, too. If she managed to live in Rio all by herself, I, too, could learn to be independent. I learn how to take care of myself and set high but achievable goals.

My mother is now back with us. But I will never forget what the experience has really taught me. I've learned a lot because of this separation. There are lots of difficult decisions that we have to face in our life. We need to have a positive attitude no matter what happens.

一只蜜蜂无法度过严寒的冬天，一群蜜蜂则不同。据说蜂箱中的蜜蜂在过冬时抱成一团，最外面一层是工蜂，他们负责拼命地煽动翅膀，像厚厚的衣服一样，阻隔着外面的寒冷，到了一定时间，另外一群工蜂就会出来同外面的工蜂换岗。在这样严实的包裹之下，里面的温度在13度左右，舒适如才春。