Q$1$: Which of the following is correct?

A$)$ The pair $(u,v),$ which is one of the minimum$-$weight edges in a graph, always belongs to a minimum spanning tree $($MST$)$ of that graph.

B$)$ The pair $(u,v),$ which is one of the minimum$-$weight edges in a graph, only belongs to a minimum spanning tree $($MST$)$ of that graph in some cases.

C$)$ The pair $(u,v),$ which is one of the minimum$-$weight edges in a graph, never belongs to a minimum spanning tree $($MST$)$ of that graph.

D$)$ The pair $(u,v),$ which is one of the minimum$-$weight edges in a graph, only exists in disconnected graphs.