第2题
A、It has been used up in producing the downward motion.
B、It has been transformed back into potential energy.
C、It has been transferred into the ball by heat.
D、It is in the ball and floor (and walls) as energy of invisible molecular motion.
第3题
A、《梧桐雨》
B、《桃花扇》
C、《长生殿》
D、《浣纱记》
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