Data on Cost, Demand and Supply for a Balanced (Total $\mathrm{X}_{i j}$

Multiple Choice

Data on cost, demand and supply for a balanced (total supply equals total demand) transportation problem is given in the table below. In the linear programming formulation of this transportation problem with $\mathrm{X}_{i j}$ denoting the amount shipped from supply point $i$ (1 or 2 $)$ to demand point $j(1,2$ , or 3 $)$ , the correct constraint to make sure that demand in demand point 1 is fully met is

A) $5 X_{11}+7 X_{21}=100$
B) $X_{11}+X_{21} \leq 100$
C) $5 X_{11}+7 X_{21} \leq 100$
D) $X_{11}+X_{21}=100$