Bipartite Graphs and Matchings · Medium problem

Four shipments $1,2,3,4$ need trucks: $1$ fits only truck $a$; $2$ fits truck $a$ or $b$; $3$ fits truck $b$ or $c$; $4$ fits only truck $c$. What is the minimum number of trucks-or-shipments needed to "touch" every (shipment, truck) compatibility listed here?