The correct option is (a) Diuretic
Easiest explanation: 1^st line treatment should continue with lifestyle modification, initial drug selection should be diuretic, beta-blocker. If inadequate, continue to second-line treatment which includes adding drugs such as Angiotensin Converting Enzyme (ACE) Inhibitor, Calcium Channel Blocker. If inadequate, continue to third line treatment increase drug dose or Substitute another drug or add a second drug from another class. If inadequate may need to do further studies serious organ damage may be present.