A. inform farmers of methods to kill insects B. recommend effective chemicals to farmers

C. decide for the farmers what to grow D. tell farmers how much money they might make

27. The central point of the text is that __________.

A. farmers hope to get high profits with high-tech tools

　　B. technology cannot control everything

C. farmers use high-tech tools at a high cost

　　D. weather is the most uncontrollable thing

C

A few years ago, Michael Scullin began teaching the science of sleep to students at Baylor University in Waco, Texas. The class centered round why the body needs to sleep and the physical and mental health problems caused by a lack of sleep. He said his students seemed to enjoy the class. But when he asked them whether they had chosen to get more sleep after what they had learned, most of them said no，so Scullin came up with a plan to get his students to sleep more.

Scullin told his students that if they agreed to sleep at least eight hours a night for the last five nights before the final exam, they would get several extra credit points. But if they agreed to take part in the study and failed to get the required amount of sleep, they would lose points. The students would wear special devices that recorded their sleep data(数据).

Only one third of all the 24 students agreed to take part in the experiment. Yet all the students who took part performed better in the exam than those who did not, even before the extra credit points were added.

Daniel Bessesen is a medical doctor who researches sleep. Bessesen notes this study supports the idea that sleeping enough helps academic performance, and students who cram are likely to be worse off. "Cramming" is a common activity for American college students. When students cram, they study most or all of the night before the exam. They get very little or no sleep because they think they will do better if the test material is fresh in their minds.

In addition, for the students who have difficulty falling asleep, Scullin offers some advice. For example, avoid looking at electronics before you are about to fall asleep and drinking anything with caffeine in it in the evening; try to go to sleep at the same time every night.

28. What can we learn from the first paragraph?

A. Michael Scullin's class focused on ways to get more sleep.

B. Michael Scullin decided to help his students get more sleep..

C. Most of the students got more sleep after Michael Scullin's class.

D. Most of the students didn't like Michael Scullin's class

29. How many students took part in the experiment?