The marketing department for an upscale retail catalog company wants to determine if there are differences in the mean customer purchase amounts across the available purchase sources (Internet, phone, or mail-in). Accordingly, samples were taken for 20 random orders for each purchase source. The ANOVA table produced shows thatSSB(sum of squares between groups) = 12715.23 andSST(sum of squares total) = 849419.93. Based on this information, state thenullhypothesis to test whether the mean purchase amount is different across the three purchase sources. Assume population 1 = Internet, population 2 = phone and population 3 = mail-in.

a.p₁=p₂= p₃=0

b.₁=₂= ₃=0

c.p₁=p₂= p₃

d.₁=₂= ₃