When the relative pronoun is the object of a preposition, which is used instead of that, for example,  in which ,  for which ,  about which ,  through which , etc. (please see the third example below): Formal English: This is the man to whom I wanted to speak and whose name I had forgotten.he relative pronoun that can only be used in restrictive clauses. It can also be substituted for who (referring to persons) or which (referring to things) in informal English. Whereas that is often used while speaking, who and which are more common in formal written English.
For other uses, see Yellowstone (disambiguation). Yellowstone National Park is a national park located in the U.S. states of Wyoming, Montana and Idaho. It was established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872. Yellowstone was the first National Park in the U.S. and is also widely held to be the first national park in the world.
Yellowstone, the world's first national park, was so named, because it was by traveling up the river of the same name into the mountains that the first explorers and writers reached it. The area was referred to as the Yellowstone region from then on, and the act of Congress setting it aside called it the tract of land in the Territories of Montana and Wyoming lying near the headwaters of the Yellowstone River. The first use of the name Yellowstone National Park was in correspondence between the secretary of the interior and the park's first superintendent Nathaniel P. Langford in 1872, according to park historian Aubrey L. Haines.