Why are the sources and effects of pollution difficult to track?

I need help plz

Now it's your turn to investigate human impact around the world. grab your virtual lab coat and put on your environmental science hat. you will be taking a trip around the globe to explore three locations. at each location, you will investigate the cause and effect relationships of deforestation, desertification, and urbanization. you will also gather evidence of how these factors have impacted the environment over time

Where do the respiratory and circulatory systems meet? a. in the heart b. in the muscles c. in the lungs d. in the brain

Which type of transport is responsible for oxygen entering into blood cells? a. vesicle b.passive c. facilitated d.active b.passive