Why is it possible to swallow while standing on one's hands?
1. Valves in the digestive system keep food from moving backward.
2. Peristalsis pushes food along the digestive tract in the right direction.
3. Bacteria clog the digestive tube and prevent food from moving in the wrong direction.
4. A wave of muscle contractions called emulsification prevents food from moving backward.

Identify the advantages and disadvantages or renewable and nonrenewable energy resources

(drag each tile to the correct location.) categorize each term as something that is typical of a scientific theory, a scientific hypothesis, or both. - a tentative statement used to guide scientific investigations. - makes predictions about future events. - can be tested by many independent researchers. - based on observations of natural phenomena. - a well-established, highly reliable explanation.

Any sound above what db can cause hearing loss in human beings