因为：f(5+t)=f(5-t)对于任意实数t都成立,所以：f(9)=f(5+4)=f(5-4)=f(1),即：f(9)=f（1）
f(13)=f(5+8)=f(5-8)=f(-3),即：f(13)=f(-3)
由题意知：f(1)＜f(-1)＜f(-3),故：f(9)＜f(-1)＜f(13) 选C
由题意知：-1 ≤ x+(1/4) ≤ 1且 -1≤ x-(1/4) ≤ 1
解-1 ≤ x+(1/4) ≤ 1得：-5/4 ≤ x ≤ 3/4 ...(1)；解-1 ≤ x-(1/4) ≤ 1得：-3/4 ≤ x ≤ 5/4...(2)
(1),(2)取交集得：-3/4 ≤ x ≤3/4,故：答案是[-3/4,3/4]