1. It is generally true that the lower the stock market falls, ________ .
2. Because aluminum is lighter and cheaper ________, it is frequently used for high-tension power transmission.
3. Within an area of only 100 miles, Death Valley sinks to 282 feet below sea level while Mount Whitney ________ to a height of 14,494 feet.
4. A good teaching technique for ________ students active is group work.
5. Isaac Newton, ________, made his discoveries about gravity nearly 300 years ago.
6. George would certainly have attended the proceedings ________.
7. Ancient civilizations such as the Phoenicians and the Mesopotamians ________ goods rather than use money.
8. The television programs we allow ________ to watch influence their learning.
9. Helen Keller lost both her sight and hearing after a severe illness ________.
10. The most exact way known to science ________ the age of artifacts is based on the radioactivity of certain minerals.
11. Studs Turkel has used what he learned ________ to produce taped oral histories of people and events.
12. One of the least effective ways of storing information is learning ________ it.
13. The theory of Continental Drift assumes that there ________ long-term climatic changes in many areas during the past.
14. Water is ________ that it generally contains dissolved materials in greater or lesser amounts.
15. From 1926 until her death, Margaret Mead ________ New York’s American Museum ofNatural History.
16. “The Good Earth”, ________, is a novel set in China.
17. In medieval times ________ his enemy to fight by throwing down his gauntlet.
18. Although most cats hate to swim, ________ if necessary.
19. Scientists believe that the beaver’s instinct to build dams is more complex than ________ other animal instinct.
20. The president usually ________ unless his press secretary approves it.