A:冰融化﹣凝固(放热)
B:雾生成﹣液化(放热)
C:露产生﹣汽化(吸热)
D:霜形成﹣升华(放热)
某种商品每件进价为20元,调查表明:在某段时间内若以每件x元(20≤x≤30,且x为整数)出售,可卖出(30﹣x)件.若使利润最大,每件的售价应为____元.
____ (lucky), his second mother was very kind to him.