18 19 A production optimization problem has 4 decision vanables and resource I limits bow many of the 4 products can be produced. Which of the following constraints reflects this fact? uit INI 25 26 27 Frish attent in Select one: O a. f{X, X2, X3, X.) 261 O b. fX1, X2, X3, X.) 5b O Cf(X, X, X3, X.) = b d. f(X1, X3, X3, X.) = b