Read the following interview with Dr John Bass, an international shark specialist who has spent many years studying sharks: First of all, doctor, are all sharks dangerous? No, they aren't. There are about 250 different kinds of sharks, but fewer than 30 of them are dangerous to humans. Certain sharks are very aggressive and we should fear them, but the danger of shark attacks is much lower than most people think. So which sharks are dangerous? The Great White shark is the most dangerous. Then there is the Tiger shark, which other sharks are afraid of, and the Blue shark. Both of them are very fast and dangerous. Which are the biggest and smallest sharks? The Whale shark is the biggest shark in the world. It grows up to 15 m in length and weighs as much as six large cars. The smallest shark, which is found near prefix = st1 /Japan, could fit into the palm of your hand because it is only 15-20 cm long. Do all sharks have teeth ? Yes, they do. Most sharks have hundreds, sometimes even thousands, of sharp teeth. These are arranged in rows of four or more. They fit quite loosely in the jaw. When the front ones break off or fall out, spare teeth move forwards from the rows behind: Sharks get a new set of teeth every two weeks. In 10 years, a Tiger may lose as many as 24,000 teeth! That's lots of teeth! What kind of food do sharks eat? Most sharks feed on small fish, and they keep the oceans healthy by eating sick and injured fish. However, hungry sharks will eat almost anything, including smaller sharks and even rubbish. Inside one Tiger shark which was found, there was a tin can, a bicycle tyre , a leather wallet and an alarm clock! And how do sharks find their food, doctor? A shark's sense of smell is excellent. It will follow the smell of blood across thousands of metres of ocean. They also see well, and they have good hearing. Sharks can feel movement in water very easily too, and it is possible for them to feel a fish moving as far as 30 m away. A shark's best sense which helps it most in finding food is its sense of _ . A) taste B) sight C) smell D) hearing
C
Contrary to people's previous knowledge, it's food shortage not dietary preference that motivates birds to migrate thousands of miles back and forth between breeding and nonbreeding areas each year, a new research shows. "It's not whether you eat insects,fruits or candy bars or where you eat them that counts,but how reliable that daytoday food source is," said the study leader W.Alice Boyle of the University of Arizona. To figure out the underlying pressure that drives some birds to leave home for the season,Boyle examined 379 related species of New World flycatchers and compared their sizes,food types, habitats, migratory behaviors and whether or not they fed in flocks. To compare the birds,the researchers constructed a "supertree" showing the exact evolutionary relationships among different species. A computer analysis then determined whether a particular species was migratory because it ran in the "family" or whether something in the bird's environment was forcing it to leave each season.Boyle and her colleagues found that food shortage was the number one issue that predicted a species' migratory behavior. "Food availability is the underlying pressure, not diet and habitat," Boyle said. An alternative strategy that the birds use to handle food shortage is to hunt in flocks, since a group is more likely to find a new source of food than an individual. "If you suffer from food shortage, you have two options," Boyle said."You can either hunt with other birds or you can migrate." For what purpose does the author write the text? A) Educating readers. B) Informing readers. C) Drawing people's attention. D) Condemning the bad environment.
B
In the mid-1950s, I was a somewhat bored early-adolescent male student who believed that _ . One day, this approach threw me into embarrassment In Mrs. Totten's eighth-grade math class at Central Avenue School in Anderson, Indiana, we were learning to add and subtract decimals . Our teacher typically assigned daily homework, which would be recited in class the following day. On most days, our grades were based on our oral answer to homework questions. Mrs. Totten usually walked up and down the rows of desks requesting answers from student after student in the order the questions had appeared on our homework sheets. She would start either at the front or the back of the classroom and work toward the other end. Since I was seated near the middle of about 35 students, it was easy to figure out which questions I might have to answer. This particular time, I had completed my usual two or three problems according to my calculations. What I failed to expect was that several students were absent, which threw off my estimate. As Mrs. Totten made her way from the beginning of the class,I desperately tried to determine which math problem I would get. I tried to work it out before she got to me, but I had brain freeze and couldn't function. When Mrs. Totten reached my desk,she asked what answer I'd got for problem No. 14. "I...I didn't get anything," I answered,and my face felt warm. "Correct," she said. It turned out that the correct answer was zero. What did I learn that day? First, always do all your homework. Second, in real life it isn't always what you say but how you say it that matters. Third,I would never make it as a mathematician. If I could choose one school day that taught me the most, it would be that one. The author could work out which questions to answer since the teacher always _ . A) asked questions in a regular way B) walked up and down when asking questions C) chose two or three questions for the students D) requested her students to finish their usual questions
A