Lightening and thunder seem very different from fog，clouds，rain，wind，heat，and other things which make up the weather.____11____ without knowing about the rest of the ____12____，one cannot understand lightening and thunder. Long ago，____13____ scientists had begun to study the weather，everyone was afraid of lightening and thunder. ____14____ the ancient Greeks and Romans，thunder was the angry voice of ____15____ great god Zeus，or Jupiter. Today we know more about weather and ____16____ lightening and thunder too，though there ____17____ still much to be learned. People today are not often afraid of thunderstorms，though we know that lightening ____18____ dangerous. ____19____ we understand lightening and thunder，there is a thrill (激动) in watching a summer thunderstorm which clears the air and leaves us ____20____. 11.[A] So [B] If [C] For [D] Yet 12.[A] weather [B] whether [C] wonder [D]wander 13.[A] before [B] after [C] since [D] when 14.[A] For [B] To [C] As [D] About 15.[A] its [B] his [C] their [D] one’s 16.[A] in [B] about [C] on [D] of 17.[A] are [B] was [C] is [D] were 18.[A] can be [B] must be [C] need be [D] should be 19.[A] While [B] Although [C] So [D] Because 20.[A] to relax [B] relaxing [C] relax [D] relaxed