是不是打错了?应该是:
A:I want some students[for]the school concert.[What]can you do,Bill?can you sing?
B:no,I[can't].But I can play the[guitar].
A:you can play the guitar!Good.Ok,what can you do,
C:I can sing (and I can play the piano.这句MS是多余的)
A:You can!Great,C.can you[piay][the][piano]?
C:No,I can it.D can[play]the piano?
A:D,can you play the piano?
D:yeah,I (can't)sing [or]dance,[but]Ican (piay) the piano.