The lecture was as dull as ditchwater.

那次讲座非常呆板乏味.

《现代汉英综合大词典》

I tried to read her latest book but found it as dull as ditchwater.

我试着读她最新的书,但发现那本书非常单调乏味.

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This novel is as dull as ditchwater, it doesn't have any decent plots.

这部小说的情节真干巴,没什么故事性.

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