In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Let me give you an example: Passage: Nearing London, Oliver encounters Jack Dawkins, a pickpocket more commonly known by the nickname the "Artful Dodger", and his sidekick, a boy of a humorous nature named Charley Bates, but Oliver's innocent and trusting nature fails to see any dishonesty in their actions. The Dodger provides Oliver with a free meal and tells him of a gentleman in London who will "give him lodgings for nothing, and never ask for change". Grateful for the unexpected assistance, Oliver follows the Dodger to the "old gentleman's" residence. In this way Oliver unwittingly falls in with an infamous Jewish criminal known as Fagin, the gentleman of whom the Artful Dodger spoke. Ensnared, Oliver lives with Fagin and his gang of juvenile pickpockets in their lair at Saffron Hill for some time, unaware of their criminal occupations. He believes they make wallets and handkerchiefs.
The answer to this example can be: Who believes Fagin's gang make wallets and handkerchiefs?.
Here is why: This question is based on the following sentence in the passage "He believes they make wallets and handkerchiefs". It evaluates the understanding that the pronoun "he" refers to name "Oliver". You can ask questions like this one about most pronouns in a paragraph.

OK. solve this:
Passage: People have used resources on and around the Mono–Inyo Craters for centuries. Mono Paiutes gathered obsidian from the Mono–Inyo Craters to make sharp tools and arrow points. Unworked obsidian was carried by the Mono Paiutes over passes in the Sierra Nevada to trade with other Native American groups. Chips of Mono–Inyo obsidian can still be found at many ancient mountain campsites.
Gold rush–related boomtowns sprang up near Mono Basin in the 19th century to exploit bonanzas. The largest of these, Bodie (north of Mono Lake), was founded in the late 1870s and grew large enough to need a tree mill, which was located at Mono Mills, immediately northeast of Mono Domes. Trees directly around the domes and on their slopes were felled to provide timber for the mill.
As part of the California Water Wars, the Los Angeles Department of Water and Power purchased large tracts of land in the 1930s within Mono Basin and Owens Valley in order to control water rights. Excavation of an 11.5-mile (18.5 km) water tunnel under the southern part of the Mono Craters dome complex started in 1934 and was completed in 1941. Tunnel workers had to deal with loose and often water-charged gravels, pockets of carbon dioxide gas and flooding. About one man was lost for each mile excavated. Water diverted from its natural outlet in Mono Lake passes through the tunnel on its way to the Los Angeles Aqueduct system.
The United States Pumice Company, based in Chatsworth, California, has mined the area for pumice since 1941. The company markets the pumice in slabs for use in commercial scouring and in large irregular chunks sold as yard decoration.Apollo 16's John Young and Charlie Duke did some of their geologic training here in June 1971.  William R. Muehlberger was one of the geology instructors.Exploratory drilling for geothermal power occurred near the Mono Craters on the south shore of Mono Lake in 1971. The wells did not show promising results, so the effort was abandoned.
Answer:
What is the full name of the company that markets pumice in slabs for use in commercial scouring?