某工地原有大小两堆沙子，共重24吨，在小堆沙子上又加入4吨，从大堆沙子里用去25％后，两堆沙子的重量正好相等，求这两堆沙子原来各是多少吨？正确的解答是（   ）

关于中纬环流的叙述，正确的是（    ）

下列关于健康的说法正确的是（　　）

任务型阅读

     My name is Chen Yang. I'm twelve years old. I'm a Chinese student.

     There are four people in my family—my father, my moth er, my brother and I. My father is a doctor at the City Central Hospital and my mother is a theatre manager. My brother is a student, too. He is thirteen. We are in the same school, but not in the same class.

I like English very much. I can speak a lot of English. I want to have an American pen friend. Let's be friends, OK? Please write to me. My address is No. 22 Middle Sc hool, Hunan, China. My email is Cheny @ hotmail. com.

阅读短文, 回答问题。

1492年，意大利航海家哥伦布的船队横渡大西洋，到达美洲。这一历史事件采用世纪纪年，应是（   ）