Consider the following shortest path problem where node $1$ is the starting node and node $6$ is the destination node.

it is a project network showing where node $1$ is starting node and node $6$ is the destination node. The nodes between node $1$ and node are the alternative nodes that can be passed.

Refer to the figure. What is the constraint associated with node $6?$

A$.$

$-$X$46+$ X$56=0$

B$.$

X$64+$ X$65-$ X$46-$ X$56=0$

C$.$

X$46+$ X$56-$ X$64-$ X$65=+1$

D$.$

X$64+$ X$65-$ X$46-$ X$56=+1$

E$.$

$-$X$64-$ X$65=-1$