Final answer:
option d,Estuaries are biomes where fresh water and salt water meet, resulting in a diluted saltwater environment with variable salinity.
Step-by-step explanation:
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted (brackish) saltwater. The salinity of estuaries varies and is based on the rate of flow of its freshwater sources. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water. This makes option b) Low salinity the correct characteristic of an estuary.
An estuary is a biome where fresh water from a river meets the salt water of the ocean. This results in brackish water, which has variable salinity. The correct answer to the characteristic of an estuary is b) an area where the salinity varies. The salinity of estuaries changes with the freshwater flow and the tidal cycles, influencing the adaptations and behaviors of the organisms living there. These organisms, including many halophytic plants and estuarine animals like mussels and clams, have developed special adaptations to survive in the fluctuating salinity conditions of their habitat.