Hi All,
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.

Since the meaning of the sentence is easy to understand let’s begin the
POE. We will identify the errors in the sentence through
POE itself.
Choice A: Just because King Alfred occupied and fortified London in 886 did not mean that he.
Incorrect. This choice is incorrect because the verb “did not mean” does not have a subject and that leads to fragment.
Choice B: The fact that King Alfred had occupied and fortified London in 886 did not mean that he had.
Correct. In this choice, verb “did not mean” has a subject “the fact” and that fact is that King Alfred had occupied and fortified London in 886.
Choice C: Just because King Alfred occupied and fortified London in 886, it did not mean he.
Incorrect. Pronoun “it” in this choice is referring to the entire preceding. This is incorrect because a pronoun cannot refer to anything but a noun or another pronoun.
Choice D: The fact that King Alfred occupied and fortified London in 886, it did not mean that he.
Incorrect. There are two errors here.
1. Subject “The fact” does not have a verb and hence we have a fragment here.
2. Pronoun “it” is again referring to the entire preceding clause.
Choice E: Just because King Alfred had occupied and fortified London in 886, it did not mean he.
Incorrect. Pronoun “it” is again referring to the entire preceding clause.
PS: Notice that the chronology of the actions in this sentence is very clear. Mention of the specific years when the actions took place establish the sequence clearly. Still the use of past perfect is preferable here because the sentence says "the fact did not mean". If it said "the fact does not mean", then we could easily do with the simple past tense.

1. When the sequence of the events is established by obvious markers, use of past perfect tense becomes optional.
2. Pronoun can only refer to a noun or another pronoun.
3. Every clause, independent or dependent must have subject-verb pair. Absence of any of the two leads to fragment error.
Hope this helps.
Thanks.
Shraddha
In the following question I am unable to apply the point no. 2. These are getting tougher. In face I eliminated option 1 as soon as I read.
Your insights required.