*Question*
Answer the following question given this paragraph: 20.5 Alternating Current versus Direct Current Alternating Current Most of the examples dealt with so far, and particularly those utilizing batteries, have constant voltage sources. Once the current is established, it is thus also a constant. Direct current (DC) is the flow of electric charge in only one direction. It is the steady state of a constant-voltage circuit. Most well-known applications, however, use a time-varying voltage source. Alternating current (AC) is the flow of electric charge that periodically reverses direction. If the source varies periodically, particularly sinusoidally, the circuit is known as an alternating current circuit. Examples include the commercial and residential power that. Q: "direct" and "alternating" are two kinds of what, which is associated with electricity? Choices: - time - constant - levels - current A:
**Answer**
current

*Question*
Answer the following question given this paragraph: Acids have some properties in common. They turn litmus, a plant extract, red. They react with some metals to give off H2 gas. They react with carbonate and hydrogen carbonate salts to give off CO2 gas. Acids that are ingested typically have a sour, sharp taste. (The name acid comes from the Latin word acidus, meaning "sour. ") Bases also have some properties in common. They are slippery to the touch, turn litmus blue, and have a bitter flavor if ingested. Acids and bases have another property: they react with each other to make water and an ionic compound called a salt. A salt, in chemistry, is any ionic compound made by combining an acid with a base. A reaction between an acid and a base is called a neutralization reaction and can be represented as follows: acid + base H2O + salt The stoichiometry of the balanced chemical equation depends on the number of H+ions in the acid and the number of OH ions in the base. Q: What type of ionic compound is formed from acid and bases reacting with each other? Choices: - isolated - common - dry - salt A:
**Answer**
salt

*Question*
Answer the following question given this paragraph: The stratosphere is the layer above the troposphere. Temperature increases with altitude in this layer. The ozone layer occurs here. Q: What is the layer above the troposphere? Choices: - thermosphere - mesosphere - troposphere - stratosphere A:
**Answer**
stratosphere

*Question*
Answer the following question given this paragraph: Triceps and biceps muscles in the upper arm are opposing muscles. Q: Triceps and biceps muscles in the upper arm are an example of what type of muscle relationship? Choices: - synchronized - symbiotic - competitive - opposing A:
**Answer**
opposing