橄榄来得便宜一些，桔子需要人工灌溉。
灌溉也没用：气候变化对人工灌溉区比雨水浇灌区的打击更大。
Irrigation may not help: climate change will hit irrigated systems harder than rain-fed ones.
目的描述人工灌溉区钉螺生长繁殖特征，为实施生态学方法控制钉螺提供理论依据。
Objective to explore the rule of growth and multiplication of snails in man made irrigation, and thus to provide evidence for snail control with ecological method.
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