| British cancer researchers have found
that childhood leukaemia is caused by an infection, and clusters of cases around
industrial sites are the result of population mixing that increases exposure.
The research published in the British Journal of Cancer backs up a 1988 theory
that some as-yet unidentified infection caused leukaemia—not the environmental
factors widely blamed for the disease. "Childhood leukaemia appears to be an unusual result of a common infection," said Sir Richard Doll, an internationally-known cancer expert who first linked tobacco with lung cancer in 1950. "A, virus is the most likely explanation. You would get an increased risk of it if you suddenly put a lot of people from large towns in a rural area, where you might have people who had not been exposed to the infection. "Doll was commenting on the new fi A. Leo Kinlen. B. Richard Doll. C. Louise Parker. D. Heather Dickinson. [填空题]Some researchers have discovered that chimpanzees have a hallmark of human culture.
[简答题]Researchers have established that when people are mentally engaged, biochemical changes occur in the brain.
[单项选择]
Researchers have found that migrating animals use a variety of inner compasses to help them navigate. Some (1) by the position of the Sun. Others navigate by the stars. Some use the Sun as (2) guide during the day, and then (3) to star navigation by night. One study shows that the homing pigeon uses the Earth’s magnetic fields as a guide (4) finding its way home, and there are indications that various other animals, from insects to mollusks (软体动物), can also make (5) of magnetic compasses. (6) is of course very useful for a migrating bird to be able to switch to magnetic compass when clouds cover the sun; (7) it Would just have to land and wait for the Sun to come out again. (8) with the Sun or stars to steer by, the problems of navigation are more complicated (9) they might seem at first. For example, a worker honeybee (10) has found a rich source of nectar and pollen flies rapidly home to the hive to 我来回答: 提交
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