Correct Answer (Detailed Explanation is Below)
A.
Clique Problem
Detailed Explanation
Clique is an NP-Complete graph problem. A clique is a subset of vertices in an undirected graph in which every pair of vertices is connected by an edge. The decision version asks whether a graph contains a clique of size at least k. A proposed clique can be verified in polynomial time, so the problem is in NP. The Clique problem is also NP-hard. Related graph problems such as Independent Set and Vertex Cover are connected through polynomial-time reductions and are important topics in computational complexity.