A Cloud of Hope and Danger

    In 2050, a small cloud floats through the air in a hospital operating room(手术室). In the room a patient, suffering from cancer, lies on a table. The cloud surrounds (包围) the patient, {#blank#}1{#/blank#}her body and filling her lungs (肺). The cloud is not smoke or steam. It is made of millions of microscopic robots called nano-robots(纳米机器人). These tiny robots move from cell(细胞) to cell in the {#blank#}2{#/blank#}body, destroying the cancer cells.

    Fighting cancer with nano-robots is only an idea today, {#blank#}3{#/blank#}scientists say that it would be possible in the future. Using nano-robots for good purposes such as fighting disease or repairing the environment may be the {#blank#}4{#/blank#}to many of today's problems.

    However, nano-robots could be a {#blank#}5{#/blank#}risk as well. Since nano-robots are so tiny, they will have to work in large teams of many thousands to 'many millions. For this reason, nano robots will have to be programmed to build {#blank#}6{#/blank#}. Scientists will not have the ability to build millions of nano-robots one by one.

    This {#blank#}7{#/blank#}to reproduce(复制)is making some scientists worried. What if something goes wrong in the programming? Quite a lot of crazy nan-orobots would be far {#blank#}8{#/blank#}than any disease. Some people think that if they get out of control, nan-orobots could destroy the Earth.

    What should be done? Should we continue{#blank#}9{#/blank#}nan-orobots or should we search for other methods? This is one of the many difficult {#blank#}10{#/blank#}that we have to make in the future.

    Imagine you are in Africa. Suddenly, a group of spots run past you fast. What is it? It may be a cheetah(猎豹) ,the fastest animal on {#blank#}1{#/blank#}. It can run up to 70 miles an hour. It is faster than most {#blank#}2{#/blank#} traveling on the highway. Although the cheetah can run fast, it uses its energy {#blank#}3{#/blank#} and becomes tired. If a cheetah can't hunt its dinner in a hurry, it will have to rest for a while before {#blank#}4{#/blank#} again.

    A cheetah is also a great hunter because its good eyesight {#blank#}5{#/blank#} it find its prey (猎物) easily. A cheetah's coat is also very {#blank#}6{#/blank#} The coat is tan(棕褐色) with black spots. This coat helps a cheetah to blend in(融入) {#blank#}7{#/blank#} the tall, brown grass in Africa. Other animals don't see it's hiding, {#blank#}8{#/blank#} a cheetah can easily catch rabbits, birds and other animals.

    Today cheetahs are facing great danger. Parts of Africa are turned into farms. This change makes cheetahs and {#blank#}9{#/blank#} animals have to find new places to live in, but that is not very easy. Other animals such as lions and hyenas(土狼) also hunt cheetahs. Luckily, zoo -keepers and wildlife experts are trying to save cheetahs. May be with their help, cheetahs will grow {#blank#}10{#/blank#} in number.

    If you visit the animal shelter (收容所) in Salinas, California, you'll see huge signs that have a picture of a dog and a cat on them. These {#blank#}1{#/blank#} are put in front of the shelter to catch people's attention. The signs {#blank#}2{#/blank#} people interested in the shelter and encourage them to visit it and maybe even take a cat or a dog into their homes.

    Each year, the shelter accepts thousands of dogs and cats. The animals are{#blank#}3{#/blank#} lost ones or left by people who can't take care of {#blank#}4{#/blank#}. Of all the animals, some of them are taken into new homes. Some {#blank#}5{#/blank#} are moved to other shelters. And, unluckily, some cannot be saved because they are too sick or are thought to be dangerous.

    Animal shelters {#blank#}6{#/blank#} food, medicine, and safe places for animals. But they are not the {#blank#}7{#/blank#} homes. The animals stay in small cages (笼子). The people who work at shelters do their best {#blank#}8{#/blank#} for the animals, but the animals do not always get the attention or exercise they need.

    To prevent animals from becoming homeless, pet owners should take good care of their pets. Most pet doctors also suggest people make {#blank#}9{#/blank#} their pets have a special surgery (外科手术). It {#blank#}10{#/blank#} animals from having more babies. And that reduces (减少) the number of homeless animals.