which answer is correct?

Below vou can see a dataset with five exolanatorv variables (plus the intercept). Originally you had only variables X2 and X3, but then you added X4,X5, and X6 much later. You noticed that this caused you a problem of perfect multicollinearity. Which of these three new variables should you discard to eliminate the problem? X4 only X 5 only X6 only X4 and X5 X4 and X6 X5 and X6 4,5 and 6