根据问题选择正确的回答
— What's this? —____;
— How many girs? —____;
— What's your name? —____;
— Is it a dog? —____;
— Where's the book? —____。
(Ⅰ)求实数a的值;
(Ⅱ)证明:函数f(x)在区间(0,+∞)上单调递减.