语法总结
过去完成时回看更早场景
great trees had covered... / the fire had been put out... 都在帮助读者区分“更早之前”和“叙事当前”。
相似句：
- The river had dried up before the rains came.
- By the time we arrived, the workers had left.
过去完成进行时写持续过程
had been fighting / had been planting 都强调某动作在过去某一时点之前已经持续了很久。
相似句：
- They had been waiting for hours when the bus arrived.
- She had been studying all night before the exam began.
not only ... but ... as well
课文用这一结构并列写出两层灾害：冲走土壤、引发洪水，逻辑非常清晰。
相似句：
- The storm not only damaged the roofs but caused power cuts as well.
- He not only apologized but offered help as well.