before : 指空间位置或时间的“在……前”。表时间时，反义词为after；指空间位置时，其反义词是behind。
- You should always wash your hands before meals.
- Before leaving he said goodbye to each of them.
- She's always up before dawn.
- Before he could reach the door, she quickly closed it.
- Before we make a decision, does anyone want to say anything else?
- She had to give the doorman a tip before he would help her with her suitcases (= he would not do it until she had given him a tip).
in front of : 指在某地方之外的前面，即不在其中，多与静态动词连用，通常可与before通用。
- She started talking to the man in front of her.
- I stood for a few moments in front of the nearest shop window.
- They put a screen in front of me so I couldn't see what was going on.
- We dried our clothes in front of the fire.
in the front of : 指在某地方之内的前面，即在其中的前部分。
- The driver sits in the front of the bus.
- Put the shortest flowers in the front (of the bunch).
- There is a table of contents in the front of a dictionary.