How many decision variables are there in a blending LP problem where we have to decide how many grams of $4$ different ingredients to blend to feed $100$ patients a diet that meets $3$ different dietary requirements? $($Note: Assume all $100$ patients will be served the same meal and have the same dietary requirements$).$

A$.3$

B$.4$

C$.7$

D$.12$

E$.$ None of these