You can’t appreciate happiness _______ you have known sadness too.[ ]

Why does she look so unhappy? — Her mother doesn’t _______ of her going to study in the United States alone.

Sorry I’m late. I got stuck in traffic. — _________. You’re here now. Come in and sit down.

Hey, Sally. Let me drive you home.–_______________, but I can walk home.

Practisig Chinese kung fu can not only ________ one’s strength, but also develop one’s character.