Though some people swear that throwing in such extras as aspirin, soda water, bleach, salt, sugar, or Karo syrup keeps trees fresher longer, the experts say plain water, and plenty of it, is best.

虽然有人信誓旦旦的说，加一些阿司匹林、苏打水、漂白粉、盐、糖或者果汁等乱七八糟的东西绝对能让树保持长时间的新鲜；但专家说了，足量的纯净的水，才是最好的。

youdao

I dare not swear "dedicated his heart stopped beating", but will try our best to service you.

俺不敢发誓“鞠躬尽瘁死而后已”，但定会竭尽全力勤勉服务于大家。

youdao

My old medical boss Dr Bolt used to swear that Colchicine, derived from crocuses, was one of the best anti-gout medicines.

BBC: 'Natural doesn't always mean best'