Why should we think that a mitochondrion used to be a free-living organism ... Based on decades of accumulated evidence, the scientific community ... The evidence suggests that these chloroplast organelles were also once free-living bacteria. ... to be the irreversible step at which the two independent organisms
It helps the plants make oxygen for us and it provides food for the plants through photosynthesis. It makes life possible on Earth by providing us light. Without light the Earth would be frozen.
The answer is C I believe
What viral disease now thought to only exist inside a laboratory caused the death of many American Indians after europeans arrived in north American?
smallpox