Extract the answer to the question from the following context. Question: Planck constant is also? Context: Classical statistical mechanics requires the existence of h (but does not define its value). Eventually, following upon Planck's discovery, it was recognized that physical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, the "quantum of action", now called the Planck constant. Classical physics cannot explain this fact. In many cases, such as for monochromatic light or for atoms, this quantum of action also implies that only certain energy levels are allowed, and values in between are forbidden.
Ans: quantum of action

Extract the answer to the question from the following context. Question: What did the named newspaper receive? Context: In March 1971, the residential office of an FBI agent in Media, Pennsylvania was burglarized by a group calling itself the Citizens' Commission to Investigate the FBI. Numerous files were taken and distributed to a range of newspapers, including The Harvard Crimson. The files detailed the FBI's extensive COINTELPRO program, which included investigations into lives of ordinary citizensincluding a black student group at a Pennsylvania military college and the daughter of Congressman Henry Reuss of Wisconsin. The country was "jolted" by the revelations, which included assassinations of political activists, and the actions were denounced by members of Congress, including House Majority Leader Hale Boggs. The phones of some members of Congress, including Boggs, had allegedly been tapped.
Ans: files detailed the FBI's extensive COINTELPRO program, which included investigations into lives of ordinary citizens

Extract the answer to the question from the following context. Question: How can the refraction index of a piece of glass be reduced? Context: Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as "crystal" when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.
Ans: by adding low-density materials

Extract the answer to the question from the following context. Question: What grows? Context: Valencia enjoyed strong economic growth over the last decade, much of it spurred by tourism and the construction industry,[citation needed] with concurrent development and expansion of telecommunications and transport. The city's economy is service-oriented, as nearly 84% of the working population is employed in service sector occupations[citation needed]. However, the city still maintains an important industrial base, with 5.5% of the population employed in this sector. Agricultural activities are still carried on in the municipality, even though of relatively minor importance with only 1.9% of the working population and 3973 hectares planted mostly in orchards and citrus groves.
Ans: orchards and citrus groves