IF I HAD KNOWN HOW TO PLAY ________ PIANO, I WOULD HAVE JOINED WIT...

15. - 20 DE TRAC NGHIEM TIENG ANH LOP 10 BAN CO BAN
20 DE TRAC NGHIEM TIENG ANH LOP 10 BAN CO BAN
15. If I had known how to play ________ piano, I would have joined with you.a. a b. an c. the d. no articleIII. GRAMMAR AND STRUCTURE : Choose the best word, phrase or sentence.