What occurs when oxygen in the lungs passes through the capillary wall to the blood, and carbon dioxide and water from the blood pass into the lungs a. respiratory system b. gas exchange c. breathing

How many chromosomes does each human cell contain? a. 23 chromosomes b. 26 chromosomes c. 43 chromosomes d. 46 chromosomes

For the strategies below, decide whether they are best described as demand-side solutions or supply-side solutions to meeting human needs for fresh water. remember that a demand-side solution reduces demand for fresh water, whereas a supply-side solution increases the supply of fresh water. (a) damming a river to create a reservoir (b) desalinating seawater (c) a nation invading a neighboring country to access their rivers (d) raising water prices for consumers and businesses (e) providing tax breaks for companies that use less water (f) replacing inefficient irrigation with more-efficient drip irrigation to grow crops (g) requiring low-flow showerheads in all new homes

Ascientific idea becomes valid when it is what?