Option B uses 'bitterness' (noun) and 'paranoia' (noun) in parallel structure, which is grammatically sound. Option C uses 'bitter' and 'paranoid' as adjectives describing Marx, also correct. Option A is incorrect because it mixes 'because of his bitterness' (prepositional phrase) with 'because he is paranoid' (clause), breaking parallelism. Since both B and C are valid constructions, D is correct.