If A is a subset of the real line R and A contains each rational number, which of the following must be true?
(A) If A is open, then A = R.
(B) If A is closed, then A = R.
(C) If A is uncountable, then A = R .
(D) If A is uncountable, then A is open.
(E) If A is countable, then A is closed.