From the Population of a University, Random Samples of 45

From the population of a university, random samples of 45 graduate students and 37 undergraduate students were given a scale that measures sexual experiences. The undergraduate students report an average of 1.6 sexual partners over their lifetimes, while the graduate students report an average of 2.5 partners. The t (obtained) for this difference was -3.56, and the t (critical) was ±2.34. Which of the following can be concluded from these observations?

A) that sexual mores are deteriorating
B) that undergraduate students are more sexually active
C) that graduate students and undergraduate students are significantly different in their sexual experiences
D) that no significant difference exists between graduate students and undergraduate students