如图所示，细绳竖直拉紧，小球和光滑斜面接触，并处于静止状态，则小球受到的力可能是

某科技小组在调查一块方圆为2hm²的草场中灰苍鼠的数量时， 放置了100个捕鼠笼，一夜间捕获了50只，将捕获的灰苍鼠做好标记后在原地放生。5天后，在同一地点再放置同样数量的捕鼠笼，捕获了42只，其中有上次标记的个体13只。则该草场中灰苍鼠的种群数量最接近（   ）

特里萨修女生于马其顿一个富裕的家庭。18岁远赴印度受训成为修女，38岁开始为加尔各答赤贫者、濒死者、弃婴、麻疯病人服务。在她的心目中，穷人同样需要尊严。1979年获诺贝尔和平奖，令世人尊敬。在颁奖典礼上，她对世人各种疑惑给予了解答：
最大的阻碍?   害怕     最严重的错误?   自暴自弃
万恶的根源?   自私     最好的休闲活动? 工作
最沉重的挫败? 灰心     最令人快乐的事? 帮助别人
最危险的人物? 说谎者   最低劣的感觉? 怨恨．
最宝贵的礼物? 宽恕     世界上最美丽的? 爱 

I usually go to school by bike，but I     to school by bus yesterday.    

根据短文理解，选择正确答案。

    During the day, you spend a lot of time running, jumping, laughing, eating, and talking. You use up a lot of energy(能量), and by the end of the day you're tired. Sleep gives your body a chance to rest.

    But your brain (大脑) and body are not completely at rest during sleep. While you sleep, your mind may think of the things that happened during the day. It keeps the important things in mind as memories(记忆). It also thinks about things you were worrying about, and you may wake up with answers to some of your problems.

    You also grow while you sleep. The thing called "human growth hormone (荷尔蒙)" in the body helps you grow during sleep. This growth hormone also helps the body to repair itself.

    Sleep helps your body to conserve energy too. You use up a lot of energy during your daily activities. But when you sleep, your body temperature falls, and your "metabolism" (新陈代谢) slows down. You are still using some energy, but much less than when you are awake and active.

    Have you ever stayed up past your bedtime? Did you have difficulty getting up the next morning? Maybe you had problems seeing clearly or you cannot think clearly. That was your body's way of saying, "I need sleep!" A lack ( 缺乏) of sleep can stop your body and mind from working correctly.