Which statement accurately compares the effects of cholera toxin and pertussis toxin?

• A. Both toxins inhibit adenylate cyclase activity.
• B. Both toxins decrease cAMP production.
• C. Cholera toxin decreases adenylate cyclase activity, while pertussis toxin increases it.
• D. Cholera toxin increases adenylate cyclase activity by inhibiting GTPase activity, while pertussis toxin increases adenylate cyclase activity by inhibiting GDP-GTP exchange.

Answer: (D)