8.
已知函数\(y=f\left( x \right)\)的定义域为\(R\),且满足下列三个条件:
\(①\)对任意的\({x}_{1},{x}_{2}∈\left[4,8\right] \),当\({{x}_{1}} < {{x}_{2}}\)时,都有\(\dfrac{f\left( {{x}_{1}} \right)-f\left( {{x}_{2}} \right)}{{{x}_{1}}-{{x}_{2}}} > 0\)恒成立;
\(②\) \(f\left( x+4 \right)=-f\left( x \right)\); \(③\) \(y=f\left( x+4 \right)\)是偶函数;
若\(a=f\left(6\right),b=f\left(11\right),c=f\left(2017\right) \),则\(a,b,c\)的大小关系正确的是\((\) \()\)