Answer:
I believe the best answer to be letter C. New screening techniques are being developed to combat computer viruses. These techniques are the subject of a new research effort at Big State University.
Step-by-step explanation:
We can readily eliminate letter B due to the inappropriate use of "nevertheless" - we do not have contrasting ideas that would justify its use.
Being left with letters A, C, and D, we can notice that letters A and D are quite ambiguous. They both use third-person plural pronouns, "they" and "them" respectively, to substitute a noun previously used. However, it is not clear if those pronouns refer to the plural noun "techniques" or to the plural noun "viruses". That is why letter C is the best option. The writer made a point of clarifying that he/she is talking about the techniques, not the viruses. Therefore, I believe the correct option to be letter C. New screening techniques are being developed to combat computer viruses. These techniques are the subject of a new research effort at Big State University.