A:Tim’s parents asked him to play the piano every day.
B:Tim and his parents would play the piano together.
C:Tim had to practice playing the piano every day.
D:to learn playing the piano is too hard for Tim.
给一无色溶液滴入数滴无色酚酞试液,溶液使酚酞变红,这说明该溶液是( )
补写出下列句子中空缺部分。