The correct answer is A. The time it takes a randomly selected student to complete an exam.
A continuous random variable is a variable that can take on any value within an interval. The time it takes a randomly selected student to complete an exam is a continuous random variable because it can take on any value between 0 and the maximum amount of time allowed for the exam.
The number of tattoos a randomly selected person has is a discrete random variable because it can only take on whole number values. The number of women taller than 68 inches in a random sample of 5 women is also a discrete random variable because it can only take on whole number values. The number of correct guesses on a multiple-choice test is a discrete random variable because it can only take on whole number values.