Which of the following sentences uses so correctly? playing tennis every day is a good way to stay in shape, so is lifting weights. traveling around the world is one of my dreams, so is visiting paris, france. walter forgot his homework, so he had to go all the way back home to get it.

The third sentence, "Walter forgot his homework, so he had to go all the way home to get it."

The last one is correct. Why?
The word "so" can be used in two ways. One is and I quote: "to such a great extent". Another is as a conjuction. Many people say the other two, but it isn't actually correct. So can only be used as a conjuction in sentences like this:
My leg hurt, so I went to the doctor.
Miss Andrews knew that I was going to have an emergency, so she let me use the bathroom.
See? You can't use so like the word "and". Hope this helps!!! (: