第三周课堂练习
Practice 1: Insert the article a or an where necessary
1.Helium is gas which consists of one proton and one neutron.
2.Labor union is organization of workers formed to improve their economic status and working conditions.
3.White dwarf is star that is unusually faint given its extreme temperature.
4.Rice is cereal grain that usually requires subtropical climate and abundance of moisture for growth.
5.Transduction is technique is which genes are inserted into host cell by means of viral infection.
6.Heat is form of energy which can be transmitted through solid and liquid media by conduction.
Practice 2: Edit the following by reducing the relative clauses where possible
1.Aluminum is a lightweight metal that is often used for high-tension power transmission.
2.Heat is a form of energy which can be transmitted through solid and liquid media by conduction.
3.A brake is a device that is capable of slowing the motion of a mechanism.
4.A dome is generally a hemispherical roof which is on top of a circular, square, or other-shaped space.
5.Snow is a form of precipitation which results from the sublimation of water vapor into solid crystals at temperatures below 0 degrees centigrade.
6． An antigen is a substance which causes
    the formation of antibodies, the body’s
    natural response to foreign substances.
7. A piccolo is a small flute that is pitched an octave higher than a standard fulte.
8. An oocyte is a cell which undergoes meiosis to produce an ovum or egg.
9. A catalyst is a substance that can speed up the rate of a chemical reaction without changing its own structure.
desiree10. A black hole is a celestial body which has approximately the same mass as the sun and a gravitational radius of about 3 km.
Practice 3: Complete the following definitions by inserting an appropriate preposition
1.A thermometer is an instrument ___ which temperature can be measured.
2.Photosynthesis is process ___ which sunlight is used to manufacture carbohydrates  from water and carbon dioxide.
3.A credit bureau is an organization ___  which businesses can apply for financial informa
tion on potential customers.
4.An anhydride is a compound __ which the elements of water have been removed.
5.An eclipse is a celestial event ___ which one body, such as star, is covered by another, such as a planet.
6.An axis is an imaginary line __ which a body is said to rotate.
Practice 4: Put the sentences into a correct order.
a.The term itself comes from the ancient Greek word palindromes meaning “running back again.”
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b.Another good and more recent example is “If I had a HiFi.”
c.Some very common English words are palindromes, such as pop, dad, and noon.
人质吉他谱d.A palindrome is a word or phrase that results in the same sequence of letters no matter whether it is read from left to right or from right to left.
e.One of the classic long palindromes is “A man, a plan, a canal, Panama.”
f.Long palindromes are very hard to construct, and some word puzzles spend immense amounts of time trying to produce good example.
Practice 5: Below you will find three pairs of sentences, each consisting of a definition and a generalization. When would it be better to begin a text with the first sentence in each pair rather than the second?
A: 1. Russian is the first language of about 150 million inhabitants of the former Soviet Union.
爱在中国    2. Russian is a language belonging to the West Slavic subgroup of the Indo-European language family.
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B: 1. A catalyst is a substance which increases the rate of a chemical reaction.
  2. Catalyst technology has progressed quickly as researchers better understand the complex interactions of molecules.
Practice 6: Label the four parts of this problem-solution text.
International students often study English for many years before going to an English speaking country to pursue a graduate degree. Their study of English usually focuses on grammar and reading, with little attention paid to speaking, writing, and listening(Belcher 1994.) Despite their many years of English instruction, after arriving in an English speaking country, many international students understandably find that their interactive skills are weak. In particular, they often experience difficulty actually using their English, which can result in frustration and misunderstanding. Recent research has shown that one way to overcome this frustration is to arrange a language exchange with a native speaker of English who wants to learn a foreign language(Brennan 1991). In this arrangement, the two partners exchange their knowledge of their native languages, thus providing a comfortable learning environment. Language exchanges can be one of the best ways to enhance one’s language skills, because they are done on a one-to-one basis.
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