Greetings!
The answer would be A. True.
Dissolved Oxygen is vital for most under water species. There has to be some flow of Oxygen throughout the water for the fish.
That is why most fish that are kept in tanks need filters. The purpose of the filter is to get that oxygen flow throughout the water, and of course keep it clean. Some fish, however will come to the top of the tank to breathe (Beta's for instance). But most fish will need that Oxygen throughout the water.
Hope this helps!