1.A bully hit Joan on her back and got away very quickly. 2.she hit him in the face.请问

1.A bully hit Joan on her back and got away very quickly. 2.she hit him in the face.请问
第一句on her back 为什么不加the,on the back,像第二题一样.
2. Mr Wu says everybody can do something for others ,For example,we can give ourseats to others on a bus .And we can also help old people or children cross the road.请问这一为什么用了一般现在时?Mr Wu says 肯定是以前说过的呀?期待你的解答