A university will add fruit juice vending machines to its classroom buildings if the student body president is convinced that more than 20 percent of the students will use them. A random sample of n students will be selected and asked whether or not they would use the vending machines. A large-sample test for proportions at the significance level of $\alpha$=0.05 will be performed. The null hypothesis that the proportion of all students who would use the vending machines is 20 percent will be tested against the alternative that more than 20 percent of all students would use them. For which of the following situations would the power of the test be highest? 
选项为:A:The sample size is n= 750, and 20 percent of all students use the vending machines.  B:The sample size is n=750, and 25 percent of all students use the vending machines.  C:The sample size is n=1,000, and 25 percentof allstudents use the vending machines.  D:The sample size is n=500, and 50 percent of all students use the vending machines.  E:The sample size is n=1,000, and 50 percent of all students use the vending machines  请回答其中一个选项.