Lucy,I can easily ______ your smiling face that the news is good.
A:refer to
B:find out
C:tell by
D:talk about
(Ⅰ)求函数 f(x) 的单调递减区间;
(Ⅱ)当 x∈(0,π2) 时,若方程 f(x)+m=0 有根,求 m 的取值范围.