Explanation: The frequency, severity, and length of heat waves are increasing. Heat and humidity already kill an average of 1,300 people in the U.S. each year. Deadly heat waves of at least 20 days affect 30% of the earth's population. That will increase to 75% by 2100 if global warming isn't stopped.
<span>B. type of matter that we cannot see but that we believe makes up more than 20% of the universe C. matter made of ordinary atoms, such as hydrogen or helium atoms </span>
