Determine the solution by using the given instructions.

Let Y1,Y2 and Y3 be 0 - 1 variables whose values indicate whether plant i is open. for i=1,2,3. In other words, for i=1,2,3,Yi=1 if plant i is open and Yi=0 if plant i is closed. Which of the following answers indicates that at least one of the plants must be open? a. Y1+Y2+Y31 b. Y1+Y2+Y31 c. Y1+Y2+Y3=1 d. Y1Y2Y3=0