Capital Co. is considering five different projects. Define Xi as a binary (0-1) variable that equals 1 if project i is undertaken and 0 otherwise, for i = 1,2,3,4,5. Which of the following represents the constraint(s) stating that projects 2, 3, and 4 cannot all be undertaken simultaneously?
a) X2 + X3 + X4 ≤ 3
b) X1 + X2 + X3 + X4 + X5 ≤ 3
c) X2 + X3 + X4 ≤ 1
d) X2 + X3 + X4 ≤ 2
e) X2 + X3 ≤ 1 and X3 + X4 ≤ 1
Answer: d