Example 2 (Question from the 9th "Hope Cup" Invitational Competition) Let the function $y=f(x)$ be an even function with a period of 2, and it is monotonically decreasing in the interval $[0,1]$. Then the size relationship of $f(-1) 、 f(0), f(2.5)$ is ( ).
A. $f(-1)<f(2.5)<f(0)$
B. $f(-1)<f(0)<f(2.5)$
C. $f(0)<f(2.5)<f(-1)$
D. $f(2.5)<f(0)<f(-1)$
Solution: Choose A. Reason: By the periodicity of $f(x)$, we have $f(-1)=f(1), f(2.5)=f(0.5)$. Furthermore, since $f(x)$ is monotonically decreasing in $[0,1]$, we know that $f(1)<f(0.5)<f(0)$, hence $f(-1)<f(2.5)<f(0)$.