A study was made to compare the plasma lactate concentration in Dutch Warmblood horses cantering at a constant speed either on a track or on an inclined treadmill. The speed was chosen as the horse's own comfortable speed on the track. Samples were taken after 5 minutes' cantering on the track and treadmill, the order of which was randomized for the 10 horses. The table below shows the plasma lactate concentrations (mmol/l): Horse 1 2 3 4 5 6 7 8 9 10 Track 2.0 7.7 4.7 4.7 1.9 2.5 5.3 4.8 3.1 3.9 Treadmill 3.5 7.2 4.6 5.7 7.5 4.4 5.6 4.6 3.5 4.9 The most appropriate approach to analyze this lactate concentration data would be a) Two-sample t-test, not assuming equal variances with a corresponding confidence interval for the difference in mean lactate levels across the two types of workouts. b) Rank Sum test with a corresponding confidence interval based on all pairwise differences across samples. c) A paired Signed Rank test with a corresponding confidence interval based on Walsh averages. d) A paired Sign test with a corresponding confidence interval based on the ordered differences