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.
Bold one happened before 'the invading Danes were well aware of this weakness and used it to their advantage in 893.'

A, C, D out


(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
Correct.
(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 <won>
'had' missing
_________________

In case you find my posts helpful, give me Kudos. Thank you.