Which do you think is more likely: humans visiting an alien planet or aliens from another planet visiting us?

Which blood cell spend most of their time in the lymphatic system?

Categorize each term as something that is typical of a scientific theory, a scientific hypothesis, or both. makes predictions

Acell in the human nervous system whose primary function is to form myelin and the blood-brain barrier, respond to injury, remove debris, and enhance learning and memory is called a(n) cell.