Classify the following pseudohistorical explanations as instances of denialism and alternative history:

Denialism:
Native Americans willingly ceded their land to the European immigrants, as evidenced by the impressive murals George Melville Smith designed in the 1930s to be displayed in U.S. post offices.
Al Gore actually won the 2000 Presidential election, because Jeb Bush (the governor of Florida) threw out thousands of Democratic votes to support the candidacy of his brother, President George W. Bush.

Alternative History:
The nineteenth-century Whitechapel Killer, also known as "Jack the Ripper," was actually an unusually long-lived serial killer who emigrated to America and was responsible for a series of murders in the late 1970s.
The frequent sightings of UFOs during the twentieth century are best explained by aliens living among us, equipped with mind-altering technology that results in most humans being unable to detect them.