What is a disadvantage of using an adjacency matrix to represent a graph with

n vertices and

m edges? a$)$ with an adjacency matrix it is slow to determine if two nodes are connected by an edge b$)$ the memory needed to store the adjacency matrix is O$($n$^2)$ regardless of the value of m c$)$ an adjacency matrix cannot support directed graphs d$)$ an adjacency matrix cannot support weighted graphs