1. Just because King Alfred occupied and fortified London in 886 did not mean that he also won the loyalty of its citizens: the invading Danes were well aware of this weakness and used it to their advantage in 893.

(A) Just because King Alfred occupied and fortified London in 886 did not mean that he

(B) The fact that King Alfred had occupied and fortified London in 886 did not mean that he had

(C) Just because King Alfred occupied and fortified London in 886, it did not mean he

(D) The fact that King Alfred occupied and fortified London in 886, it did not mean that he

(E) Just because King Alfred had occupied and fortified London in 886, it did not mean he

The OA is B. Whats wrong with A

You can't use a phrase starting with "because" as a NOUN. Choices A and C are of the form "NOUN did not mean that...," so A fails this test. "Fact," on the other hand, is clearly a noun, so you're good there.

For the same reason, you can't say "the reason for X is because Y", since the form there is "the reason for X is NOUN." (There's also a redundancy issue.)

Incidentally, the GMAT would probably shorten the correct answer even further, to "That King Alfred occupied and fortified London in 886 did not mean that..." This construction, starting with "That..." is called a noun clause; it's rather tricky.

D is a run-on, and C and E both contain an "it" that doesn't refer to anything in particular.