下列函数中指数函数的个数是( ) ①y=2x; ②y=x2; ③y=2x+1; ④y=xx; ⑤y= (6a-3)x. A.0 B.1 C.2 D.3 答案:C 解析:只有①⑤是指数函数;②底数不是常数,故不是指数函数;③y=2x+1=2×2x是2与指数函数y=2x的乘积;④中底数x不是常数,它们都不符合指数函数的定义.Harry Potter only had a small room ____ when he just came to his aunt’s.Choose the wrong answer :A.to sleepB.to sleep inC.in which he could sleepD.where he could sleep