2. 外语
  3. A project likely to evolve in the near or intermediate future is space tourism. Today space tourism has become a pure commercial

A project likely to evolve in the near or intermediate future is space tourism. Today space tourism has become a pure commercial

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问题     A project likely to evolve in the near or intermediate future is
space tourism. Today space tourism has become a pure commercial【S1】______
activity that would not have to rely unpredictable government【S2】______
decisions. It would therefore put space operations on a much more
solid, dependable footing and would enormously expand man’s space
activity. If some people see space tourism as a potential multibillion-【S3】______
dollar business, difficult technical problems remain to be sobered.
    First, in order to fulfill the dream of space tourism, a
manned reusable rocket like the Venture Star must be built.
Then, the second serious problem must be addressed; Even【S4】______
today’s most-advanced space rockets are able to lift only about
2. 5% of their launch weight into orbit—a ratio that has hardly
changed in the last 40 years. But it is simply impossible to find【S5】______
other alternations other than a rocket. This unsatisfying fact is a【S6】______
result of the limits of material characteristics and chemical power
sources, and there is no indication which any fundamental【S7】______
breakthrough can be expected in these areas in the foreseeable
future. Then these who have long-cherished dreams of space tourism【S8】______
have to wait forever.
    Operational costs may be somewhat reduced by the use of air-
breathing engines to help a reusable rocket penetrate into earth’s
atmosphere. Today the highest cost attainable to lift a payload to【S9】______
orbit is more than $ 4,000 per pound; the price of a ticket to space
would have to be at least $ 50,000. It is questionable whether a
sufficient number of customers could be tempted to pay so a high【S10】______
price for a short trip around the world.
【S2】
选项
答案rely∧一on／upon
解析 介词缺失。rely是不及物动词，表示“依赖，依靠”应使用短语rely on／upon。
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