Input: Article: Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid, while standard grid electricity can be used to meet shortfalls. Net metering programs give household systems a credit for any electricity they deliver to the grid. This is handled by 'rolling back' the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility then rolls over the kilowatt hour credit to the next month. Other approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter. Most standard meters accurately measure in both directions, making a second meter unnecessary.

Now answer this question: Why is a second meter usually unnecessary to monitor electricity use?

Output: Most standard meters accurately measure in both directions

Input: Article: The firm continued to pressure Kelsey and the agency to approve the application—until November 1961, when the drug was pulled off the German market because of its association with grave congenital abnormalities. Several thousand newborns in Europe and elsewhere suffered the teratogenic effects of thalidomide. Though the drug was never approved in the USA, the firm distributed Kevadon to over 1,000 physicians there under the guise of investigational use. Over 20,000 Americans received thalidomide in this "study," including 624 pregnant patients, and about 17 known newborns suffered the effects of the drug.[citation needed]

Now answer this question: How many Americans were given the drug Kevadon?

Output: Over 20,000

Input: Article: In the United States, federalism originally referred to belief in a stronger central government. When the U.S. Constitution was being drafted, the Federalist Party supported a stronger central government, while "Anti-Federalists" wanted a weaker central government. This is very different from the modern usage of "federalism" in Europe and the United States. The distinction stems from the fact that "federalism" is situated in the middle of the political spectrum between a confederacy and a unitary state. The U.S. Constitution was written as a reaction to the Articles of Confederation, under which the United States was a loose confederation with a weak central government.

Now answer this question: On the political spectrum, where does federalism stand? 

Output:
federalism" is situated in the middle of the political spectrum between a confederacy and a unitary state