经典例题233 when they analyzed these rocks，they foundshockedquartz grains—slivers with a particular arrangement of micro cracks believed to represent the relic left by an extraterrestrial impact.分析：when引导的时间直接翻译为在…的时候。
经典例题234 as land developed，rain water and rivers dissolved salts and other substances from rocks and carried them to the oceans，making the ocean salty.分析：as在句中引导的是一个时间状语从句。
参考译文在陆地形成时，雨水和河水溶解了岩石中的盐和其他物质并把它们带入海洋，使海水变咸。
（2）根据语境确立译法
经典例题235 the story dated back to one night in march，1993，when mr.and mrs.shoemakers went to an observatory near san diego，california to observe heavenly bodies till dawn.
