1. In back of means located behind.
Pattern 1: noun + in back of + noun
There is a beautiful tree in back of our house.
Pattern 2: verb + in back of + noun
Your sister sits in back of me in class.
For beautiful and naturally pink lips, it is very important that you always keep your body hydrated. It is best to increase your water intake and include a lot of fresh fruit juices in your diet as it would keep your lips healthy and soft.