One adaptation that is unique to marine mammals is they nurse their young.. The correct option among all the options that are given in the question is the fourth option or the last option or option "d". I hope that this is the answer that you were looking for and the answer has come to your desired help.
In the mitochondria of the cell
For example salt in water ,salt would dissolve ,you won't be able to see it but if you taste it it would still be there
dissolve /disappear but still be there
