There are 5 multiple choice questions on an exam, each having responses a, b, c, or d. Each and every question is worth five points, and only one potion per question is correct. Suppose the student guesses the answer to each question, and his or her guesses from question to question are independent. The student's mean number of questions correct on the exam should be
A. 1.25
B. 2.5
C. 6.25