The company produces 3 different products. If X_ab = the production of product a in period b, then to indicate that the limit on production of the company's 3 products in period 1 is 350, we write:

a. X₃₂ 350

b. X₁₁ + X₂₁ + X₃₁ 350

c. X₁₂ + X₂₂ + X₃₂ 350

d. X₃₁ + X₃₂ + X₃₃ 350

e. None of the above