When analyzing the correlation between Percent Attendance and Letter Grade, why is the Spearman correlation the only option? a) The Spearman correlation must be used when one variable is ratio and the other is ordinal

b) The Spearman correlation must be used when one variable is ratio and the other is dichotomous

c) The Spearman correlation must be used when both variables are dichotomous

d) The Spearman is not the only option; you can use the Pearson as well