Option E is actually quite interesting and has good learning. It says:
....the United States bought it for about four cents an acre, more than doubling the country's size and bringing its western border within reach of the Pacific Ocean.
It is important to note that the fact that United States bought Louisiana for about four cents an acre had
no bearing (was
not the reason) on doubling the country's size and bringing its western border within reach of the Pacific Ocean.
GMAT does test this concept in some cases. A very interesting example that comes to mind:
Emily Dickinson’s letters to Susan Huntington Dickinson were written over a period beginning a few years before Susan’s marriage to Emily’s brother and ending shortly before Emily’s death in 1886, outnumbering her letters to anyone else.
The reason this sentence is
incorrect is because the fact that those letters where written "
over a specific period", was
not the "
reason" why these letters outnumber her letters to anyone else.