Which biome contains both freshwater and salt water? a. lake b. estuary c. river d. ocean

The answer should be B. estuary.

B. estuary

Explanation:

An estuary is a biome which is formed at the site where the freshwater from a river or lake source combines with the saline water of the ocean. As a result of this the water in the estuary can be either fresh or saline depending upon the volume of water present higher from either of the source.  

The organisms living in this biome are adapted to survive in both fresh and salt water. They are adapted to survive when the salinity of the water drastically increases in the biome.

the answer is d.) homologous; have mammary glands