Which of the following is a concrete message?

A. "Get this out of here." is vague and abstract because it does not specify what “this” is or where it should go. B. "When is she coming home?" is unclear since “she” is not identified. C. "They said it is too early to get in." is ambiguous because “they” is not defined and the situation is not explained. D. "Help me put this pile of books on Marsha's desk." is a concrete message because it clearly identifies what needs to be done (help), what the object is (pile of books), and where it should go (Marsha’s desk).