The problem with E is the pronoun it, which can only refer to a singular noun coming before it in the sentence. The only singular noun "it" could refer to is the Louisiana purchase, which doesn't make sense - the US didn't buy the purchase for 4 cents an acre - it bought acres for 4 cents an acre.

Pronoun is dangerous - whenever you see a pronoun such as "he, she, they, it, this", ask yourself:

1) What does the pronoun refer to? does it agree with the noun it is supposed to refer to? (pronoun agreement error)

2) Does the pronoun have more than one noun coming before it that it could possibly refer to (pronoun ambiguity error).

hope this helps.