The degree of a vertex is defined as the number of edges that touch the vertex. The (i, j)-th entry of the adjacency matrix tells you whether vertex i touches vertex j (1 if yes, 0 if no). Then the degree of vertex i is equal to the sum of the i-th row in the adjacency matrix.
• vertex 1 : degree = 0 + 1 + 0 + 0 + 1 = 2
• vertex 2 : degree = 1 + 0 + 1 + 1 + 1 = 4
• vertex 3 : degree = 0 + 1 + 0 + 1 + 0 = 2
• vertex 4 : degree = 0 + 1 + 1 + 0 + 1 = 3
• vertex 5 : degree = 1 + 1 + 0 + 1 + 0 = 3
So, the correct answer is A. 2.
