Bipartite Graphs and Matchings · Medium problem

Eight items sit in a network: items $1$ and $2$ can each only be paired with item $a$; items $3$ and $4$ can each only be paired with item $b$; item $5$ can only be paired with item $c$ (and $a,b,c$ are $3$ more items in the network, for a total of $8$). What is the size of a maximum independent set among all $8$ items (the largest group with no possible pairing between any two of its members)?