Mark the letter A, B, C, or D that needs correction: Before (A) the invention4/15Mark the letter A, B, C, or D on your answer sheet to show the underlined part that needs correction. Before (A) the invention of the printing (B) press, books have been (C) all printed by hand (D).Beforethe printinghave beenby handGiải thíchĐáp án C.