Based on my research, freshwater fish are a type of fish that has a higher concentration of salt than it's internal environment. With respect to osmoregulation, to fight this circumstance the freshwater fish has a kidney that makes the water to pass quickly.
B. Macromolecules is the answer.
Answer: B- Bacteria
Explanation: Bacteria are infinitesimal organisms that have single cells that grow in different atmospheres. They have an easily understood inside arrangement. Their cells are normally surrounded by two shielding coverings which are an external cell continuous vertical structure and a cell pliable sheet-like structure acting as a boundary inside. However, some bacteria do have a third shielding sheet furthest from the center named the capsule.