Consider the transportation table below with two sources and five destinations. Unit costs for each shipping route are in dollars.

$$

Destination

Source

A

B

C

D

E

Supply

$1$

$$$$12$

$$$$8$

$$$$5$

$$$$10$

$$$$4$

$18$

$2$

$$$$6$

$$$$11$

$$$$3$

$$$$7$

$$$$9$

$14$

Demand

$6$

$8$

$12$

$4$

$2$

Besides$$ non$-$negativity and integer$$ constraints, how many constraints does this transportation problem$$ have?

A$.$

None of the options

B$.$

$17$

C$.$

$10$

D$.$

$7$