Corn variety 1 yielded 140 bushels per acre last year at a research farm. This year, corn variety 2, planted in the same location, yielded only 110 bushels per acre. Based on these results, is it reasonable to  conclude that corn variety 1 is more productive than corn variety 2? 

a. Yes, because 140 bushels per acre is greater than 110 bushels per acre.

b. Yes, because the study was done at a research farm.

c. No, because there may be other differences between the two years besides the corn variety.

d. No, because there was no use of a placebo in the experiment.

e. No, because the experiment wasn’t double-blind.