Consider the following maximal flow problem where node $1$ is the source and node $6$ is the destination.

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

Refer to the figure. What is the objective function?

A$.$

Max X$61$

B$.$

Min X$16$

C$.$

Max X$26+$ X$56$

D$.$

Max X$16$

E$.$

Min X$61$