An equestrian enthusiast is interested in the racing times of horses. She believes an older horse will have a faster race time than a younger horse. She selects a random sample of 17 sibling pairs of adult horses and records their times for running on the same track. The mean difference (Older - younger) in the times to run the track is -15.7 seconds with a standard deviation of 8.3 seconds. What are the hypotheses the equestrian should use?

a. H₀ : μDᵢ = 0;Hα : μDᵢ < 0
b. H₀ : μDᵢ = 0;Hα : μDᵢ > 0
c. H₀ : μₒₗₑᵣ= μᵧₒᵤₙₑᵣ; Hα : μₒₗₑᵣ > μᵧₒᵤₙₑᵣ
d. H₀ : μₒₗₑᵣ= μᵧₒᵤₙₑᵣ; Hα : μₒₗₑᵣ < μᵧₒᵤₙₑᵣ