The correct answer is D. secretive.
The word “nefarious” means evil or wicked. The word “progressive” means moving forward or developing. The word “systematic” means done or happening according to a fixed plan or system. The word
“secretive” means keeping something secret or hidden.In the context of the question, Pakistan has been vigorously pursuing a clandestine nuclear weapons programme. This means that Pakistan has been working on developing nuclear weapons in secret. This is a secretive activity because Pakistan does not want other countries to know about it.
The other options are not correct because they do not accurately describe the activity that Pakistan is engaged in. Pakistan is not evil or wicked, it is not developing nuclear weapons in order to move forward or develop, and it is not doing so according to a fixed plan or system. Pakistan is simply trying to keep its nuclear weapons program a secret.