The last pages of the September 1999 publication The Code

Meaning wise, this topic is a disaster, with so many ambiguities and uncertainties. A book can contain only one last page, not several last pages. One must use “the last few pages” if several passages are intended.
Actually what are decipherable are the encrypted messages and not the pages or the languages. Even in the most grammatically correct choice B, the topic messes up this fact by using an adjectival modifier that may modify the subject of the sentence namely pages or the object of the preposition, namely the languages, because of proximity.
To say that the pages comprised a brainteaser because they were written in a puzzle does not convey much meaning.
On the grammar side, the picture is somewhat clear, thankfully.
A is a fragment with two verbs for a subject; B is acceptable C and E mess up the meaning with the wrong use of past perfect and D missing the symmetrical parallelism on either side of the ‘and’ .