单选题 Which of the following contributes to the low-cost of using rainwater?

A、 Rainwater is free of chemical treatments.
B、 People have been harvesting rainwater for centuries.
C、 The water harvesting system is built on a platform.
D、 Rainwater can be collected using pipes.

【正确答案】 A

【答案解析】第二段第三句Unlike ground water，rainwater contains no minerals or salts and is free of chemical treatments。和地下水不同，雨水不含矿物质或盐类，因此无需化学处理。据此推理，使用雨水可省去化学处理费用，成本自然较低。