阅读理解。
根据短文内容, 从短文后各题所给的四个选项中选择最佳选项，将其代号填入题前括内。
One day a poor farmer was taking a bag of rice to town. Suddenly the bag fell from his horse
on the road. He didn't know what to do about it because it was too heavy for him to lift (举起) by
himself. He only hoped that somebody would soon pass (经过) by and help him.
Just at this moment a man riding a horse came up to him. But the farmer was very disappointed
(失望的)when he saw who he was. It was the great man living nearby. The farmer had hoped to ask
another farmer or a poor man like him for help.
But to his surprise, the great man got off his horse as soon as he came nearer. He said to the
farmer, "I see you need help, friend. How good it is that I'm here just at the right time," Then he took
one end of the bag, the farmer took the other. They together lifted and put it on the horse.
"
Sir," asked the farmer, "how can I pay you?"
"It's quite easy," the great man answered with a smile, "Wherever (无论在哪里) you see anyone
in trouble, do the same for him."
1.What happened when the farmer went to town?
A. His horse's leg was hurt.
B. The bag fell from his horse.
C. The farmer lost his bag.
D. His bag was stolen.
2. The farmer didn't lift the bag onto the horse by himself because .
A. the bag was broken
B. the horse went away
C. the bag was too heavy
D. the farmer was ill
3. Why was the farmer very disappointed when he saw the great man? Because he thought the great man .
A. couldn't see him
B. could take away his bag
C. could take away his horse
D. couldn't help him
4. Who helped the farmer?
A. A great man.
B. Another farmer.
C. A poor man.
D. A friend.
5. What does the story mainly (主要地) tell us?
A. Everybody should become a great man.
B. We should help the man who is in trouble.
C. Everybody couldn't do as the farmer did.
D. We should pay for other's help.
，波长
。a、b、c、d是介质中4个质量相等的振动质元。由此可知
时刻，4个质元中动能最大的为d