英语六级攻克阅读关键句229. Prices fluctuate, in response to harvests

229. Prices fluctuate, in response to harvests, natural disasters and political instability; and when they rise, it takes some time before new sources of supply become available.

译文　价格由于收成、自然灾害和政局的动荡而波动；当价格上升时，得过一段时间后才会出现新的供应源。

点睛　本句的主干是Prices fluctuate...；it takes some time...。其中，in response to引导原因状语；before引导时间状语从句。

fluctuate意为“波动，变动”。本句中的in response to为固定短语，意为“作为对……的回应”。如：

He only shrugged his shoulders in response to the question. 他只是耸了耸肩，作为对问题的回答。

instability意为“不稳定；不安定”。如：

The riot can be considered a symptom of political instability. 这次暴动可以看做政治上不稳定的征兆。