广告好比一把钥匙用英文怎么说

Advertisement is a key (to open the gate of sth)
其实不一定要加“like”，翻译的时候可以结合上下文，避免逐字翻译，使得整体英文更加流畅

Advertising is like a key.
这就是你要的答案，仅供参考。
对你有助，别忘加分啊!

Advertisement is just like a key.