Dinosaurs were reptiles which became extinct about 65 million years ago. The most intriguing question about dinosaurs has always been " (21) did they die out" There is no simple answer to this question, (22) many hundreds of scientists are studying the problem. They are not studying the extinction of the dinosaurs (23) , but the whole question of extinction. Many other plants and animals have (24) in the past, and it is important to understand (25) this happened. Having this information could help save many species that are (26) in the modern world. Humans are causing extinctions now, because of pollution and other damage (27) the environment. Maybe the dinosaurs can tell us how to save the earth today, (28) their extinction 65 million years ago! Some of the early dinosaur scientists, 100 years ago, thought the dinosaurs died out because the (29) changed, and they could not breathe. Others thought that the d
A. themselves
B. by themselves
C. alone
D. only
Passage One
The making of glass is a very old industry--at least 4,500 years old. Glass has many extraordinary qualities and it is frequently being used in new ways.
One of the most interesting new uses for glass is in telephone communication. Scientists have developed glass fibers as thin as human hair, which are designed to can-y light signals. When the light reaches the other end, it is first changed into electrical signals, which are in turn converted into sound messages.
Called light wave communication, the new system was used successfully in an experiment in Chicago in 1997. During the experiment, two glass fibers were able to carry 672 conversations at the same time. The lightwave cable, containing 144 glass fibers, has the capacity to carry 50,000 conversations at the same time.
The lightwave communication system has two important advantages. First, the glass fiber cables are smaller and weigh less than copper. Second, they cost less
A. glass fiber is less expensive
B. glass fiber delivers messages directly
C. glass fiber is more up to date
D. glass fiber is easier to make
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