They compare the number of mutations to determine how long ago species separated and evolved.
Most fish (especially the "Bony fish") achieve neutral buoyancy through a sac called the swim bladder in there body of which is filled with air, not much but it'a just enough to keep then a float. The fish can control this organ, and using that they can fill or release air to allow them to rise or sink.
Cartilaginous fish however, do not have a swim bladder.
hope this helps :)
<span>nerve impulses
hormones</span>
The answer is d. Pandemic
It is pandemic because it is spreading globally