下列有关肺泡适于进行气体交换特点的叙述正确的是．（    ）

①肺泡数量很多   ②肺泡外面包绕着丰富的毛细血管  

③肺泡壁和毛细血管壁都是由一层上皮细胞构成    ④肺泡分布广泛．

关于在空中水平射出的子弹，下列说法正确的是（不计空气阻力）（   ）

公元前6世纪，鲁国某贵族有封地300亩，另辟新荒地200亩，按规定他应向国家交税的田亩数是

    My name is Sam. I am a junior high school student. My school is close to my home, so I always go to school on foot. Classes start at 8 a.m., and I am seldom late. I like Geography best. I enjoy learning about different places in the world.

    In the morning, we usually study Chinese, Maths and English. We have our morning break at 9:50 a.m..  When the bell rings, I run to the playground with my best friends Tom and Jack. We often play games. Break ends at 10:10 a.m..

Lunch is from 11:50 a.m. to 12:30 p.m.. Afternoon classes end at 3:30 p.m. Then Tom, Jack and I take part in the school bank practice. We make great music together.

    I always have a good time at school.