尿道的作用当然是让一条河流通过它。
The purpose of the urethra is certainly to have a river run through it.
今天，河流控制的原因有很多，主要是为了维持可靠的水资源供应，以满足日常生活、农业和工业、发电、航行的用水需要，并起到防洪作用。
Today, rivers are controlled for many reasons, primarily to maintain reliable water supplies for daily, agricultural and industrial needs, for power generation, for navigation, and to prevent flooding.
森林因其提供的多方面产品，在很多方面都有着重大作用，西方纳税人需要亚马逊热带雨林帮助控制气候变暖，巴西人需要雨林让河流长流水，让水力发电机能发电，亚马逊流域的豆农需要雨林带来足够的降水。
Western taxpayers need the Amazon rainforest to control their climate. Brazil needs it to help feed its rivers and generate hydro-power.
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