7880. Pakistan has been vigorously pursuing a clandestine nuclear weapons programme.

✅ The correct answer is option D.
Nefarious : (typically of an action or activity) wicked or criminal.

Progressive : happening or developing gradually or in stages.

Systematic : done or acting according to a fixed plan or system; methodical.

Secretive : (of a person or an organization) inclined to conceal feelings and intentions or not to disclose information.

Clandestine : kept secret or done secretively, especially because illicit.

Synonym of Clandestine is Secretive