8. Colin decided to investigate soil erosion by water. He measured rates of erosion on model hills made of soil, rock, and sand. Which of the following
was the test (independent) variable? *

economic impact of malaria is estimated to cost africa $12 billion every year. this figure factors in costs of health care, absenteeism, days lost in education, decreased productivity due to brain damage from cerebral malaria, and loss of investment and tourism.

trachea, alveoli, lung capillaries, arteries