I believe the awncer is B
Answer: In Medieval Europe, knights pledged loyalty to vassals, who in turn pledged theirs to powerful lords, and serfs labored in the fields.
Explanation:
A rigid hierarchy refers to one where people who are born into a certain position in life, find it quite hard to move from it or rather one where there are different social classes and people had to be classified in one class for the system to work.
The system during medieval times was much like this. Social classes existed that determined a person's worth in society such as the knights, vassals, Lords and Royals. There was also the serfs who were considered the lowest in the hierarchy.
A biome is defined as the large ecological area where the formation of plants and animals with common characteristics gather due to the similar climates. If I were an ecologist, and i will be determining whether an entire river and lake biome is being threatened by human activity, the indicator species that i might look for are the ones that have been introduced into the biome.
Answer: Sustainability is important for a very simple, very straightforward reason: we cannot maintain our quality of life as human beings, the diversity of life on Earth, or Earth’s ecosystems unless we embrace it. There are indications from all quarters and from the smallest to the largest scale that sustainability is something we must address.
