谁帮我作下阅读谢了Animals perform many useful and entertaining jobs.D

谁帮我作下阅读谢了
Animals perform many useful and entertaining jobs.Dogs are particularly valuable in guiding the blind (a trained dog can learn never to cross a busy road when cars are coming,even if his master command him to do so),protecting property,finding lost people,and bunting criminals.Horses are used in guarding herds,carrying men in lands where there are no roads,and helping farmers work their land.Pigeons have long been used to carry message.Wild animals from the jungles,forests and seas are very popular performers in circuses and moving pictures.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 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 comes to deliver letters.One explanation for this behavior is that although the postman comes to the house often,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 postman can easily show the dog that the postman is a friend and that 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 understanding correctly.
16.A dog feels 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
17.Dogs who accompany blind people must learn ________.
A.to obey all orders
B.to obey only safe orders
C.never to cross busy road
D.to cross roads when commanded
18.Which of the following shows training a watchdog often bring about unexpected result?
A.Some dogs attack guests.
B.Some dogs don't know the postman.
C.Some dogs just sit and stay there.
D.Some dogs will attack the postman.
19.Some dogs always attack the postman,because ________.
A.they don't know the postman are friends
B.the dogs are not the watchdogs
C.the postman never enters the house
D.the dog's masters never welcome the postman
20.Sometimes dogs can _______.
A.send mails B.help the blind
C.find lost purse D.help drive a car
17题 为什么不选 不是更直接说了？

16 B And a dog is always happy when he is praised for understanding correctly.
17 B (a trained dog can learn never to cross a busy road when cars are coming,even if his master command him to do so),引申
18 D However,some dogs will always attack the postmen who comes to deliver letters.
19 C One explanation for this behavior is that although the postman comes to the house often,he never enters the house
20 B Dogs are particularly valuable in guiding the blind
17题,never to cross a busy road when cars are coming,明显,当有车过来的时候不会穿马路,而且根据文章理解,这只是安全信号的一种~