8.已知a=log3.43.5+log3.53.4a=\log _{3.4}3.5+\log _{3.5}3.4a=log3.43.5+log3.53.4,b=log3.53.6+log3.63.5b=\log _{3.5}3.6+\log _{3.6}3.5b=log3.53.6+log3.63.5,c=logπ3.7c=\log _{\pi }3.7c=logπ3.7,则((( )))