What is the constraint for node $3$ in the following maximal flow problem?

Question $10$Select one:

A$.$

$$ X$34+$ X$13+$ X$23=0$

B$.$

$$ X$34+$ X$23=0$

C$.$

$$ X$34+$ X$13=0$

D$.$

$$ X$34$ X$13$ X$23=0$