Read the following passage and mark letter A, B, C or D to indicate the correct answer to each of the questions that follow.
Solar energy is a long lasting source of energy which can be used almost anywhere. To generate solar energy, we only need solar cells and the sun. Solar cells can easily be installed on house roofs, so no new space is needed and each user can quietly generate their own energy. Compared to other renewable sources, it also possess many advantages. Wind and water power rely on turbines which are noisy, expensive and easy to break down. Solar cells are totally silent and non-polluting. As they have no moving parts, they require little maintenance and have a long lifetime.
However, solar energy also has some disadvantages. We can only generate solar energy during daytime because the system depends on sunlight. Besides, solar cells require large area to work effectively. The main disadvantage of solar energy is that it costs about twice as much as traditional sources such as coal, oil, and gas. This is because solar cells are expensive. Scientists are hoping that the costs of solar cells will reduce as more and more people see the advantages of this environmentally friendly source of energy.
Which of the following is the MAIN disadvantage of solar energy mentioned in the passage?
A.Solar cells require large areas to operate. 
B.It depends on sunlight.
C.It is expensive.   
D.It is unfriendly to the environment.

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Read the following passage, and mark the letter (A, B, C or D) on your answer sheet to indicate the correct answer to each question.
 Human memory, formerly believed to be rather inefficient, is really more sophisticated (63)than that of a computer. Researchers approaching the problem from a variety of points of view have all concluded that there is a great deal more stored in our minds than has been generally supposed.(65) Dr. Wilder Penfield, a Canadian neurosurgeon, proved that by stimulating their brains electrically,(66) he could elicit  the total recall of specific events in his subjects’ lives. Even dreams and other minor events supposedly forgotten for many years suddenly emerged in detail.
The memory trace is the term for whatever is the internal representation of the specific information about the event stored in the memory. Assumed to have been made by structural changes in the brain, the memory trace is not subject to direct observation but is rather a theoretical construct that we use to speculate about how information presented at a particular time can cause performance at a later time. Most theories include the strength of the memory trace as a variable in the degree of learning, retention, and retrieval possible for a memory. One theory is that the fantastic capacity for storage in the brain is the result of an almost unlimited combination of interconnections between brain cells, stimulated by patterns of activity(68) Repeated references to the same information support recall. Or, to say that another way, improved performance is the result of strengthening the chemical bonds in the memory.
All of the following are true of a memory trace EXCEPT that
A.it is probably made by structural changes in the brain
B.it is able to be observed
C.it is a theoretical construct
D.it is related to the degree of recall