Inner signals control other biological clocks. German scientists found that some internal one seems to order birds to begin their migration flights two times each year. Birds prevented from flying become restless when it is time for the trip. But they become calm again when the time of the flight has ended.

A mix of outside and internal events controls some biological clocks; such things as heartbeat and the daily change from sleep to walking take place because of both external and internal signals.

Scientists are beginning to learn which parts of the brain contain the biological clocks. A researcher at Harvard University ─ Dr. Martin Moore Ede ─ said a small group of cells near the front of the brain seems to control the timing of some of our actions. Probably there are other cells to control other body activities. He is studying how they affect the way we do our work. Most of us have great difficulty if we must often change to different work hours. It can take many days for a human body to accept a major change in work hours. Industrial officials should have a better understanding of biological clocks and how they affect workers. He said such an understanding could reduce sickness and accidents at work, and would help increase production.

26. Which of the following can not be controlled by biological clocks?
[A] Dreams.
[B] when and what to eat.
[C] Body temperature.
[D] When the flowers should open.

27. The author mentions Siberian hamster to illustrate that _________.
[A] every living thing has a biological clock
[B] Siberian hamster is a highly adaptive species
[C] biological clocks can change an animal's skin color
[D] external factors can affect the behavior of an organism

28. From the passage we can infer that __________.
[A] biological clocks are responsible for all the human behaviors
[B] biological clocks are too mysterious to be explained
[C] heartbeat and some daily activities affect biological clocks
[D] studies on biological clocks can throw some light on human actions

29. Why should industrial officials have a better understanding of biological clocks?
[A] Because some cells in the brain are very important.
[B] Because it is very hard to change working time.
[C] Because it may lead to improvement of work efficiency.
[D] Because it takes a long time for a person to get used to the shift of work hours.

30. The best title for the passage could be _________.
[A] A Brief Account of Biological Clocks
[B] Biological Clocks and Work Efficiency
[C] How Biological Clocks Work
[D] The location of Biological Clocks

Passage Three
Questions 31 to 35 are based on the following passage.

"There is no arguing about taste"─ runs the Latin proverb. But taste did not just happen. Cultural, historical, biological and environmental events have interacted to cause frogs, for example, to be viewed as delicious in southern China but to be regarded with revulsion(厌恶)in northern China. Even though much remains unknown, tastes cannot be dismissed as inarguable or illogical; an attempt will be made here to discover why, as Lucretius put it,"What is food to one man may be fierce poison to others?"