demi lovato的on the line是和jonas brothers中哪一个唱的啊？还是都有对唱过？哪一段是哪一个唱的啊?

当然是两个主唱都有啦。不过Nick只有两句（never would've said forever, if i knew we'd end so fast.
baby i just can't hear what you're saying.）
，决大部分是Joe。