21、 阅读材料，回答21-40题。
No one knows how man learned to make words. Perhaps he began by making sounds like those made by animals. Perhaps he grunted like a pig when he lifted something heavy. Perhaps he made sounds like those he heard all round him-water splashing, bees humming, a stone falling to the ground. Somehow he learned to make words. As the centuries went by, he made more and more new words. This is what we mean by language.
People living in different countries made different kinds of words. Today there are about fifteen hundred different languages in the world. Each contains many thousands of words. A very large English dictionary, for example, contains four or five hundred thousand words. But we do not need all these. Only a few thousand words are used in everyday life.
The words you know are called your vocabulary. You should try to make your vocabulary bigger. Read as many books as you can. There are plenty of books written in easy English for you to read. You will enjoy them. When you meet a new word, find it in your dictionary. Your dictionary is your most useful book.
From this passage, we know that________
A．man never made sounds
B．man made animal sounds
C．man used to be like animals to make sounds
D．man learned from the animals to make sounds


22、 The number of different languages spoken is about________
A．150
B．1,500
C．5,000
D．4,000


23、 People from different countries________
A．made same words
B．made different kinds of words
C．had a same language
D．used some sounds


24、 Man to make sounds.________
A．used words
B．followed many things in nature
C．lifted heavy things
D．grunted like a pig


25、 You can enlarge your vocabulary by________
A．reading more books
B．finding new words in dictionaries
C．writing more
D．using the words in everyday life


26、 阅读材料，回答26-45题。
Spending 50 minutes with a cell phone close to your ear is enough to change brain cell activity in the part of the brain closest to the antenna (天线 ). But whether that causes any harm is not clear, scientists at the National Institute of Health said at a conference last month, adding that the study will not likely settle concerns of a link between cell phones and brain cancer. "What we showed is glucose(葡萄糖metabolism(代谢)( a sign of brain activity) increases in the brain in people who were exposed to a cell phone in the area closest to the antenna," said Dr. Nora Volkow of the NIH, whose study was published in the Journal of the American Medical Association. The study was meant to examine how the brain reacts to electromagnetic fields caused by wireless phone signals.
Volkow said she was surprised that the weak electromagnetic radiation (电磁辐射）from cellphones could affect brain activity, but she said the findings do not shed any light on whether cellphones cause cancer. "This study does not in any way indicate that. What the study does is to show the human brain is sensitive to electromagnetic radiation from cell phone exposures. " Use of the devices has increased dramatically since they were introduced in the early 1955s, with about 5billion cell phones now in use worldwide.
Some studies have linked cell phone exposure to an increased risk of brain cancers, but a large study by the World Health Organization did not offer a clear answer to this. Volkow’s team studied 47 people who had their brain examined while a cell phone was turned on for 50 minutes and another while the phone was turned off. While there was no complete change in brain metabolism, they found a 7 percent increase in brain metabolism in the region closest to the cell phone antenna when the phone was on.
Experts said the results were interesting, but urged that they be understood with great care. " Although the biological significance, if any, of increased glucose metabolism from too much cell phone exposure is unknown, the results require further investigation," Henry Lai of the University of Washington in the U. S. and Dr. Lennart Hardell of University Hospital in Sweden, wrote in an article in JAMA. "Much has to be done to further investigate and understand these effects." They wrote.
According to the passage, which of the following is TRUE?
A．Cell phone use is dangerous.
B．Cell phone use causes cancer.
C．The human brain is an electromagnetic field.
D．There are about 5 billion cell phone users in the world right now.


27、 Doctor Volkow was astonished because_______
A．her research has shed light on her understanding of cell phone
B．she found that cell phone exposure is harmful to human brain
C．she found that using a cell phone for about 50 minutes could influence or change brain activity
D．human brain is not responsive to electromagnetic radiation


28、 According to the passage, cell phones were launched_______
A．in the late 1970s
B．between 1955 and 1960
C．in the late 1955s
D．in the early 1990s


29、 What does the word "that" stand for in the second paragraph?
A．Brain activity.
B．Her research findings.
C．The fact that cell phone use may cause cancer.
D．Her research progress.


30、 Which of the following is an appropriate title for this passage?
A．Cell Phone Radiation: Is It Harmful?
B．Cell Phone Radiation: Is It Useful?
C．Cell Phone Radiation: Is It Healthy?
D．Cell Phone Radiation: Is It Weak?