单选题 Animals do many useful and entertaining jobs. (38) Dogs are particularly valuable in guiding the blind (a trained dog can learn never to cross a busy street when cars are coming, even if his master commands him to do so), protecting property, finding lost people, and hunting criminals. Horses are used in guarding herds, carrying men in lands where there are no roads, and helping farmers plow fields. Pigeons have long been used to carry message. Wild animals from the jungles, forests and seas are very popular performers in circuses and movies. People realize that, although animals may not have the same intelligence as human beings, they are smart enough to learn certain things.
The first thing a dog is taught is to obey. It should not take too long for him to learn commands. Simple orders, such as "sit, lie down, stay there, come here" can even be taught by a child.
Training a dog to be a watchdog often produces unexpected results. Some dogs quickly learn the difference between unwanted people and friends. This is because their masters welcome friends and invite them into their houses. However, some dogs will always attack the postmen who come to deliver letters. One explanation for this behavior is that, although the postman comes to the house frequently, he never enters the house. Therefore, the dog thinks the postman is someone who is not wanted, but keeps coming back anyway.
Masters of dogs who attack postmen can easily show the dogs that the postman is a friend and the dog does not need to treat him as an unwanted person. A dog is quite ready to do what his master wishes. And a dog is always happy when he is praised for proper understanding.

单选题 A dog feels the happiest if, after he has worked well,______.
A. he gets a good piece of meat
B. he gets praise from his master
C. he is allowed to be by himself
D. he is taken for a walk in the evening

单选题 Dogs who accompany blind people must learn______.
A. to obey all orders B. to obey only safe orders
C. never to cross busy roads D. to cross roads when commanded

单选题 Which of the following shows that training a watchdog often brings about unex-pected result?
A. Some dogs attack guests.
B. Some dogs don't know the postmen.
C. Some dogs just sit and stay there.
D. Some dogs will attack the postmen.

单选题 Some dogs always attack the postman because______.
A. they don't know the postman is a friend
B. the dogs are not the watchdogs
C. the postman never enters the house
D. the dog's masters never welcome the postman

单选题 Sometimes dogs can______.
A. send mails B. help the deaf
C. help the blind D. help drive a car