Let p and q be two non-empty disjoint subsets of r. which of the following is (are) false? could someone explain this question?

Let P and Q be two non-empty disjoint subsets of R. Which of the following is (are) FALSE? (A) IfP and Q are compact, then P uQ is also compact (B) IfP and Q are not connected, then PuQ is also not connected (C) IfPUQ and P arc closed, then Q is closed (D) IfP UQ and P are open. then Q is open