A store manager wishes to investigate whether there is a relationship between the type of promotion offered and the number of customers who spend more than $30 on a purchase. Data will be gathered and placed into the two-way table below.

Which statement best describes how the manager can check if there is an association between the two variables?
a)The manager must check relative frequencies by row because there are more than two different promotions.
b)The manager must check relative frequencies by column because there are more than two different promotions.
c)The manager cannot use relative frequencies to look for an association because there are more than two different promotions.
d)The manager should check both relative frequencies by row and by column to look for an association.