a) option is correct
Step-by-step explanation:
Homeostasis is the way animals maintain a stable internal balance in their body and allows animals to function in the changing external conditions surrounding their body
The high salt concentration in the ocean means that salt will be constantly diffusing into the body of some animals
Water and salts can move through the gill membrane to maintain the balance
The kidneys are used to remove excess salts through their urine, which is quite concentrated
The concentrated urine is also due to the increase in a hormone (ADH) which causes more water to be reabsorbed by the kidneys