Astyle manual gives this rule for formatting years and centuries:

spell out centuries in lower case. for spans of years, separate the beginning and ending years with an en-dash.

which sentence correctly follows the rule?
question 3 options:

did the twentieth century span the years 1900 to 1999 or the years 1901 to 2000?

did the twentieth century span the years 1900–1999 or the years 1901–2000?

did the twentieth century span the years 1900–1999 or the years 1901–2000?

did the twentieth century span the years 1900 to 1999 or the years 1901 to 2000?