Please submit the rest of the question please :)
Answer:
The Great Lakes and Corn Belt occupies a significant portion of this subregion located between the Appalachian Mountains to the east and the Rocky Mountains to the west named A. America’ s central lowlands.
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.
Answer:
b. flat rotation curves in spiral galaxies
Explanation:
Dark matter accounts for majority of the matter in the universe (about 85%). It is considered to be composed of subatomic particles which are yet to be discovered. Dark matter cannot be observed because it does not emit light that can be detected. Only its gravitational effect is visible.
Astronomers when calculated the mass of the visible matter and tried to account for the observed speed of stars in the galaxy, there was a mismatch. To understand what caused this mismatch, astronomers gave name to the invisible matter as the Dark Matter.
The expected velocity of stars should decrease away from the near the center of the galaxy but a constant velocity of stars was observed that is a relatively flat rotation curve was obtained.
Thus, flat rotation curves in spiral galaxies in an evidence of Dark Matter.
