A pharmaceutical company has developed a newdrug that they believe could improvestudents' performance on a statistics exam. To test the drug's effects, they randomly select 30 students, give half of them a control substance (group 1), and give the other half the drug (group 2). Both groups take the statistics exam, and the graph below portrays the resulting group mean scores.Remember they are expecting an improvement in the experimental group.The drug company sets their significance level (alpha) to .05 for the hypothesis test between the two groups (group 1 = no drug/Control; and group 2 = drug/Experimental). This hypothesis test requires a(n):

a. Repeated Measurest-test

b. Single sample Z test

c. Single sample t test

d. Independent sample t-test