You must never show this secret key to anyone else.

Let's exchange keys tomorrow.

He is good at playing the black keys.

She played the white keys of the piano briskly.

He is posting private tweets by creating a private account.

Please make sure to lock the door before you leave the house.

The key to success is in your own hands.

This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.

Believing that failure is a stepping stone to success, he challenged again.

Believing that failure leads to success, he continued to challenge himself over and over again.