单选题 What does the word "precursor" in the context in Para. 3 mean?

A、 A man that may come before the happening of an earthquake.
B、 The leading actor that may cause a series of events to occur.
C、 An meaningful sign that indicates some would-be happenings.
D、 An event that may have symbolic or significant nature.

【正确答案】 C

【答案解析】[精解] 本题为词义辨析题。考生可以在上下文中得到提示。首先提到了“so， finding one all-purpose warning sign is impossible．”紧接着下文提到，即使找到了a quake precursor，还是很难对所有危险的地震做出预警。可见，在这里precursor 意为a meaningful sign 比较合适。