A Fleet of Rental Cars - All the Same Make $25.9$

A fleet of rental cars - all the same make, model, and year - has a mean fuel efficiency of $25.9$ miles per gallon (mpg) . A random sample of 51 cars are selected and the air filter of each is replaced with a new one. Let $\mu$ be the population mean fuel efficiency score that would occur if every car's air filter were replaced. The air filter change is deemed effective if $\mu > 25.9$ mpg. A test is made of $H _ { 0 } : \mu = 25.9$ versus $H _ { 1 } : \mu > 25.9$ . Consider these possible conclusions:
i) . The air filter changes are effective.
ii) . The air filter changes are not effective.
iii) . The air filter changes might not be effective.
Which of the three conclusions is best if $H _ { 0 }$ is not rejected?

A) iii
B) $\mathrm { i }$
C) $\mathrm { ii }$