翻译：“香港是中国的一个城市，这是常识。”

It is common sense that Hong Kong is a city of China.

It's common knowledge that Hong Kong is a city in China.

anngelyun - 总监 九级的答案比较规范...其他人的都不错,只是"常识"一般翻译为COMMON SENSE会更为合理.

it is a common knowledge that HONG KONG is a city of China.

it is common knowledge that honkong is a city of China

It's known that Hong Kong is a city of China.