A high school math teacher gave her 30 students a math exam. In this exam, the average scores for the high school students in the United States is 48.00. If she sets the significant level as 0.05, and she wants to know if her students' performance are different from the students in the United States, the type of data analysis and the critical value for this test are:
A. z-test, ±1.645
B. z-test, ±1.96
C. t-test, df=29, ±1.699
D. t-test, df=29, ±2.045