14．下列说法正确的是

A．收音机的原理：通过改变接收机的频率选出需要的无线电信号，这是电谐振现象．把接收到的信号进行调制、放大，通过扬声器还原为声音

B．电子束通过某一晶体窄缝时可能产生衍射图样

C．一切物体都在向外辐射红外线，物体温度越高，辐射红外线越强，波长越长

D．自然光是光振动沿各个方向均匀分布的光，偏振光是光振动沿着特定方向的光

A．若已知人造地球卫星的轨道半径和它的周期，利用引力常量，就可以算出地球质量

B．两颗人造地球卫星，只要它们的绕行速率相等，不论它们的质量、形状是否相同，它们的绕行半径和绕行周期一定是相同的

C．两颗人造卫星一前一后在同一轨道上沿同一方向绕行，若要后一卫星追上前面卫星并发生碰撞，只要将后者速率增大一些即可

D．在绕地球飞行的宇宙飞船中，若宇航员从舱内慢慢走出，并离开飞船，此飞船的速率不会因质量减小而改变

第一节：短文改错(满分10分)

　 下面短文中有10处语言错误。请在有错误的地方增加、删除或修改某个单词。

增加：在缺词处加一个漏字符号(∧)，并在下面加上该加的词。

删除：把多余的词用斜线(\)划掉。

修改：在错的词下划一横线，并在该词下面写上修改后的词。

注意：1. 每处错误及其修改均仅限一词；

　　　 　　 　2. 只允许修改10处，多者(从第11处起)不计分。

例如： It was very nice to get your invitation to spend ∧ weekend with you. Luckily 　　　　　　　　　　　　　　　　　　　 the I was completely free then, so I’ll to say “yes”. I’ll arrive in Bristol at around 8 p.m. am in Friday evening. on

Today I’d like to tell you anything about riding a bike in London. If you visit London, you’ll

see many buses, cars or bikes. It’s very cheap and quick to use bike. If you take a bus, I often have to wait for an hour or so. Besides, the buses move very slowly. The underground is quickly but expensive and often crowded. I used to travel to work by bus. I was often late, and tiring. Then a friend suggested we went to work by bike. I followed him. Although we went slowly, but we always arrived on time. Taking a bus takes 50 minutes, while ride a bike only half an hour. Now I love riding to work and I feel more better.