题目内容：
Natural gas is recognized as the most economical energy source ____________
参考答案：
答案解析：
单选题：Natural gas is recognized as the most economical energy sour
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简述杂货班轮货运程序。
简述杂货班轮货运程序。
San Francisco is fully prepared for another big earthquake.A
San Francisco is fully prepared for another big earthquake.A. Right B. Wrong C.
根据下列材料请回答题：The San Francisco area is located above several a
根据下列材料请回答题：The San Francisco area is located above several active fault lines.A.
What's the author's view about flattery?
What's the author's view about flattery?
请回答（2）题。
请回答（2）题。