The answer is B.
Im pretty sure water is important for some organisms.
Density is mass of object per unit volume
Most of the ways to stop invasive animal species from entering the Great Lakes ecosystem is starting with people themselves. try not to plant anything that would be invasive to the echo system and also try helping out by cleaning out the Great Lakes by picking up litter and so forth
1. Rhythm generators (SA node)
2. Conductive cells (node cells)
3. Contractile cells (myocardial cells)
