A true/false test has 20 questions. Each question has two choices (true or false), and only one choice is correct. Which of the following methods is a valid simulation of a student who guesses randomly on each question. Explain.

a. Twenty digits are selected using a row from a random number table. Each digit represents one question on the test. If the number is even the answer is correct. If the number is odd, the answer is incorrect.

b. A die is rolled 20 times. Each roll represents one question on the test. If the die lands on a 6, the answer is correct; otherwise the answer is incorrect.

c. A die is rolled 20 times. Each roll represents one question on the test. If the die lands on an odd number, the answer is correct. If the die lands on an even number, the answer is incorrect.