13. Scientists have discovered that the jellylike material in cells __________ proteins and other substances. a. is actually a complex mixture b. it is actually a complex mixture c. actually is a complex mixture of d. that actu

9. __________ food we eat lacks minerals, then the body can use the stores from its bones for more urgent needs. a. As the b. If the c. The d. Since

8. __________ the world’s most successful artificial language. a. As Esperanto is b. That Esperanto c. It is Esperanto d. Esperanto is

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10. __________ an organism to become a fossil. a. Rarely b. It is rare c. Rare is d. It is rare for

4. An enzyme works by coming in contact with a particular substance, __________ with it, and changing it. a. combines b. combining c. it combines d. to combine

1. The behavior of many volcanoes __________ very difficult to predict, especially the more explosive types. a. are b. is c. that d. being

11. Among sea horses, __________ carries and hatches the eggs in a special breeding pouch. a. it is the male which b. the male it c. it is the male d. the male who

12. __________ will be increasingly used as a source of petrochemicals when oil begins to run out. a. No matter coal b. No doubt coal c. If coal d. That coal

14. The discovery that electricity could produce magnetism __________ in 1820 by the Danish physicist, Hans Christian Oerested. a. by accident b. was an accident c. was made by accident d. by accident was

2. __________ more than 2,000 minerals are known, nearly all rocks are formed from seven mineral groups. a. Although b. However c. Despite d. Since A

15. Digital systems work first by changing quantity and then __________ into strips of numbers. a. convert the measurements b. the measurements convert c. to convert the measurements d. converting the measurements