I would say that the answer is #2
The sentence needs commas because the participial phrase is essential.
Answer:
Fish are a great pet to have. They are fun to watch as they swim around the tank you put them in. Although fish tanks, heaters, filters, and other supplies aren't super cheap, the best part, the fish, are not very expensive at all. And the more you get into it the better it becomes. You may start with a 3-gallon tank and end up with a 20-gallon tank.
Explanation:
A verb is a a word used to describe an action, state, or occurrence.
1. Wow look at that globe
2. The globe shows the world
3. The globe is round
4. We are inside the globe
5. There is green spots everywhere on the globe
