¡¡¡¡From 1947 to 1969 the U.S. Air Force investigated UFOs as a possible threat to national security. A total of 12,618 reports were received, of which 701 reports, or 5.6 percent, were listed as unexplained. The air force concluded that "no UFO reported, investigated, and evaluated by the Air Force has ever given any indication of threat to our national security". Since 1969 no agency of the U.S. government has had any active program of UFO investigation.
¡¡¡¡Some persons, however, believe that UFOs are extraterrestrial spacecraft, even though no scientifically valid evidence supports that belief. The possibility of extraterrestrial civilizations is not the stumbling block; most scientists grant that intelligent life may well exist elsewhere in the universe. A fully convincing UFO photograph has yet to be taken, however, and the scientific method requires that highly speculative explanations should not be adopted unless all of the more ordinary explanations can be ruled out.
¡¡¡¡UFO enthusiasts persist, however, and some persons even claim to have been captured and taken aboard UFO's. No one has produced scientifically acceptable proof of these claims. Behavioral scientist Carl Sagan once proposed that "certain psychological needs are met by belief in superior beings from other worlds".
1. What is the significance of the UFO sighting in 1947 according to the passage?
A) It was the first evidence showing the existence of intelligent life outside Earth.
B) It helped to explain some sightings of unusual events occurring in the sky.
C) It aroused widespread interest in unidentified flying objects in the sky.
D) It started off a new era of flying saucers in the United States.

2. The second paragraph of the passage focuses on
A) some explanations about UFO sightings.
B) different kinds of UFOs reported.
C) people's negative reaction to UFOs.
D) interesting claims made about UFOs.

3. According to the passage, which of the following about the UFO investigation by the U.S. Air Force is NOT true?
A) About 84 percent of the UFO reports received were explained.
B) UFOs were once regarded as a potential danger to national safety.
C) There was no evidence that the U.S. was being threatened by the reported UFOs.
D) No hard evidence supported the existence of UFOs.

4. According to the passage, the belief that some UFOs are spaceships from some extraterrestrial civilizations
A) has been supported by a convincing UFO photograph.
B) would be accepted if it met the requirements of the scientific method.
C) has been regarded as some kind of creative thinking.
D) Has ruled out other explanations about the origin of UFOs.

5. Why did Carl Sagan think there are so many UFO enthusiasts?
A) The belief in UFOs gives them psychological satisfaction.
B) The explanation that UFOs are only conventional objects is not attractive.
C) They are strongly influenced by science fiction and science fiction films.
D) Curiously makes them accept the speculative explanations about UFOs.

Key: CCABA

PASSAGE 46

Pollution around the House

¡¡¡TScientists are closely concerned with the structure of buildings and with the quality of building materials. The World Health Organization (WHO) observes that the introduction of air conditioning and energy conservation measures have been accompanied by growing problems of indoor air quality. Some pollutants arise from insulation products, some from moving cars, and others from modern housing materials. As many Europeans spend up to 90% of their lives in buildings, the health effects of the indoor climate are very important.

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