There are several chemical factories waste water into the river.Apour B．pouring C．pours

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解析：
本题的完整句子应为There are several chemical factories that/which are pouring waste water into the river,本题是同时省略主语和谓语，只留下pouring,故选Ｂ，Ｃ为第三人称的单数明显错误，因为前面的主语工厂是复数。