What did Jan Baptista van Helmont's five-year willow tree investigation demonstrate ?

What is the leading cause if water scarcity throughout much of the world

"what factors influence the absorption of sunlight at earth's surface? "

Which source would provide the most bias-free information about smoking and increased health risks? a) a website created by heart disease patients b) a research study conducted by the mayo clinic eliminate c) a public service message sponsored by tobacco companies d) an online question forum conducted by attorneys for cardiac specialists