violin,piano可数吗?如果可数,为什么只说playing the violin,playing the pia

violin,piano可数吗?如果可数,为什么只说playing the violin,playing the pia She likes playing the violin I am playing the violin. 是he plays the violin 还是he playing the violin he is playing the violin变为一般现在时 My sister is playing the violin now. my brother likes playing the violin ,too. I am practicing playing the violin.有语病吗? he piano ,likes,violin,playing,both ,the,and,连词成句 he is playing the violin .对划线部分提问,划线部分：playing the violin 请问是playing piano 还是playing violin呢? I am playing the violin.改成一般疑问句?