The correct answers are B. impenetrable and E. unfathomable.

Explanation
- Logic: The sentence sets up a contrast with "yet." Although the lectures contain "flashes of extraordinary penetration" (deep insight), the "tortuous syntax" and heavy translation make large parts of the argument nearly impossible to understand. The clue "all but the most dogged exegetes" (critical interpreters/explainers of text) tells us that only the most determined scholars can crack the text. Therefore, we need two synonyms that mean impossible to understand or pierce through.
- Vocabulary:
- Impenetrable means impossible to understand; unfathomable. This perfectly fits how a dense, poorly translated text behaves.
- Unfathomable means incapable of being fully explored or understood. Together with impenetrable, it forms a perfect Sentence Equivalence pair.
- Abstruse means difficult to understand or obscure. While it fits the context of the sentence beautifully, it lacks a proper synonym among the other choices to form an equivalent pair (impenetrable and unfathomable are much tighter synonyms for text that is completely closed off to readers).
- Meretricious means apparently attractive but having in reality no value.
- Pellucid means translucently clear, which is the exact antonym of what is needed.
- Soporific means tending to induce drowsiness or sleep. While a tortuous text might make someone sleepy, it doesn't match the logical requirement of being readable only by expert exegetes.