The answer should be B. The main concept that be leveraged here to eliminate answers is Comparison. The Pali Canon is literature collection (like a collection of book) and can be compared with Books. While Theravada Buddhism, which is a religion, can be compared with Western Religions.
(A) The Pali Canon, the collection of the scriptures of Theravada Buddhism, easily would fill a large bookcase, unlike the three great Western Religions, which have single book scriptures, and it is ironical because Buddhism is much less text-based than are their Western counterparts.
Reason to eliminate - The Pali Canon and the Western religions are being compared here, which is not the right comparison
(B) In contrast to the single-book scriptures of each of the three great Western Religions, the Pali Canon, the collection of the scriptures of Theravada Buddhism, easily would fill a large bookcase, although ironically, Buddhism is much less text-based than are its Western counterparts.
Correct Answer - Comparison is logical
(C) Unlike the single-book scriptures of each of the three great Western Religions, Theravada Buddhism has a scripture collection, the Pali Canon, that easily fills a large bookcase, although Buddhism with irony is much less text-based than are their Western counterparts.
Reason to eliminate - The comparison is between single book (for Western religions) and religion Theravada Buddhism.
(D) Buddhism is much less text-based than the three great Western Religions, having a single book scripture each, but the Pali Canon, the collection of the scriptures of Theravada Buddhism, would fill a large bookcase ironically.
Reason to eliminate - We have -ing modifier issue mainly. The expression "having a single book scripture" is describing the way why Buddhism is less text based --> Which is not the logical & intended meaning
(E) The three great Western Religions each have a single book scripture, but ironically, Theravada Buddhism, having a scripture collection, the Pali Canon, that would fill a large bookcase, despite the fact that Buddhism is ironically less text-based than are their Western counterparts.
Reason to eliminate - There are multiple issues, but the easiest reason to eliminate this one is --> There is no verb for Pali Canon