In an Introductory Science Class, 80 Student Volunteers Were Randomly

In an introductory science class, 80 student volunteers were randomly assigned, in equal number, to take a class for a letter grade or for a simple pass/fail grade.At the end of the semester, the mean achievement score for the letter grade group was 86.2 and for the pass/fail group 79.8.The calculated t = 4.60, p<.001.The results should appear in a published report as follows:

A) Introductory science students have significantly higher achievement scores when awarded letter grades rather than a simple pass/fail grade.
B) There is no significant difference in the achievement scores of introductory science students when awarded letter grades or a simple pass/fail grade.
C) Students are more motivated to achieve when given letter grades rather than simple pass/fail grades.
D) Instructors should use letter grades rather than pass/fail grades for introductory science courses.
E) a and d