Most dogs have an easy life in the U. S. They eat, play, get attention from their     _________and sleep. But some dogs work hard. They are called guide dogs. Guide dogs help___________people move from place to place safely.

Guide dogs and their owners are a___________. Guide dogs don’t lead the owners, and their owners don’t___________control the guide dogs. They work together. The guide dogs don’t know where the owners want to go, so they___________the owners’ instructions. The owners can’t see the obstacles (障碍物) along the way, so the dogs make decisions for the___________of the owners. Guide dogs stop at all crossroads before___________a street. They don’t see color, so they don’t know if the light is red or   ___________The owners decide if it is time to cross the street by listening to the sound of     ___________. The dogs help the owners get on a bus or train. They learn to____________many tasks.

Most guide dogs are very____________and friendly. A guide dog needs to work     ____________distraction(分心) in noisy places, bad weather, crowds of people, and____________situations. When you see a guide dog, it is important that you____________that the dog needs to focus on (集中于）its job. Don’t pet or talk to the dog.____________is very difficult, and it requires a dog’s full____________Guide dog training lasts about five months. Only about 72 percent of dogs that enter the training program “graduate”. Those that graduate bring their owners valuable____________and love. In other dog training programs, trainers use____________as a reward. In guide dog training, the trainers don’t use food. They use physical affection (爱抚). This is____________a guide dog sometimes takes the owner to a restaurant. It must lie____________at the owner’s feet without wanting to eat.

Oscar, a two year old cat, lives in a nursing home, where people stay when they are very ill or at the end of their lives. Every day, Oscar ______ in and out of the patients’ rooms. The nurses say that he is just like a ______. He looks at each patient and ______. Then he usually leaves the room. ______, when Oscar decides to stay and gets on the bed next to the patient, the nurses ______ the doctor and the patient’s family. According to the nurses, Oscar has accurately ______ the death of 25 patients so far.

Oscar’s story is just a story. ______ has done research to ______ how accurate Oscar really is. However, two research studies have found that some dogs can ______ cancer.

In the first study, cancer patients ______ into tubes. Researchers then ______ five dogs to sit or lie down ______ they smelled the breath samples with cancer. Next came the ______ test. The dogs smelled more than 150 different breath samples. On average, they ______ 93 percent of the cancer samples.

In the second study, several dogs identified a sample that the researchers ______ was cancer-free. The researchers sent it back for more lab tests. This time, the tests showed that the sample ______ did show signs of cancer. The dogs identified cancer that the first tests ______!

What makes dogs a species of animal that is so ______ detecting cancer? Diseases such as cancer produce smells. Dogs can ______ as much as 10,000 times better than people.

Will a visit to the doctor soon include a sniff from a friendly animal? Some people think this is not a(n) ______ idea. It is less expensive than a lab test, and it doesn’t hurt!

Many animals move from one place to another at certain times of the year. This _______ movement is called migration (迁徙). They migrate to _______ food, or in search of warmer weather. One of the most wonderful migrations in nature is that of the North American monarch butterfly.

Every _______, millions of these beautiful insects with fine black and orange wings begin a long and _______ journey. Somehow they manage to _______ around 4,000 kilometres _______ and find their way to California or Mexico. _______, until recently no one knew how they did this. A team of scientists led by Professor Eli Shlizerman at the University of Washington has now found the _______. They have found out that the monarch is able to _______ the time of day. It uses its eyes to measure the ________ of the sun. These two pieces of information allow the ________ to determine the way to go. ________, it manages to reach where it will spend the winter.

The solution to the mystery of the monarch’s amazing ability comes at a time when it is in serious trouble. Its ________ has crashed by as much as 90 per cent in the last few years. ________, human activity is the main reason why the number of monarch butterflies is falling. The research on the monarch’s ________ has however led to a greater awareness of this creature.