like: der Schlüssel → →
der Schlüssel ☊ 
chìa khóa ☊ 
☊ the key/crucial/deciding factor ☊ factor ☊
The key doesn't fit the lock. ☊ fit ☊
key (to sth): The key to success is preparation. ☊ key ☊
The key is, how long can the federal government control the inflation rate? ☊ key ☊
Good communication is key to our success. ☊ key ☊
The key has stuck in the lock. ☊ stick ☊
The key turned stiffly in the lock. ☊ stiffly ☊
The key is hanging on a string by the door. ☊ string ☊
Confidence is the key to success. ☊ success ☊
the key to the door ☊ to ☊