Answer the following question given this paragraph: Heat below Earth's surfacecalled geothermal energy can be used to produce electricity. A power plant pumps water underground where it is heated. Then it pumps the water back to the plant and uses its thermal energy to generate electricity. On a small scale, geothermal energy can be used to heat homes. Installing a geothermal system can be very costly, however, because of the need to drill through underground rocks. Q: What do you call the heat below earth's surface that can be used to produce electricity? Choices: - inert energy - renewable energy - natural energy - geothermal energy A:
geothermal energy

Answer the following question given this paragraph: Many pathogens that cause respiratory diseases spread by droplets in the air. Droplets are released when a person sneezes or coughs. Thousands of tiny droplets are released when a person sneezes ( Figure below ). Each droplet can contain thousands of pathogens. Viruses that cause colds and the flu can spread in this way. You may get sick if you breathe in the pathogens. Q: How many pathogens can each droplet contain? Choices: - tens - billions - hundreds - thousands A:
thousands

Answer the following question given this paragraph: Isotopes of Hydrogen Hydrogen, the most abundant element in the universe, is the ultimate source of all other elements by the process of nuclear fusion. (For more information on nuclear fusion, seeChapter 20 "Nuclear Chemistry". ) Table 21.2 "The Isotopes of Hydrogen" compares the three isotopes of hydrogen, all of which contain one proton and one electron per atom. The most common isotope is protium (1H or H), followed by deuterium (2H or D), which has an additional neutron. The rarest isotope of hydrogen is tritium (3H or T), which is produced in the upper atmosphere by a nuclear reaction when cosmic rays strike nitrogen and other atoms; it is then washed into the oceans by rainfall. Tritium is radioactive, decaying to 3He with a half-life of only 12.32 years. Consequently, the atmosphere and oceans contain only a very low, steadystate level of tritium. The termhydrogen and the symbol H normally refer to the naturally occurring mixture of the three isotopes. Table 21.2 The Isotopes of Hydrogen. Q: What is the most abundant element in the universe? Choices: - carbon - helium - nitrogen - hydrogen A:
hydrogen

Answer the following question given this paragraph: Pluto has three moons of its own. The largest, Charon, is big compared to Pluto. The Pluto-Charon system is sometimes called a double dwarf planet ( Figure above ). Two smaller moons, Nix and Hydra, were discovered in 2005. Q: How many moons does pluto have? Choices: - six - two - four - three A:
three