A random variable X can take on the value 0, 1, 2, or 3. Which of the following is a possible probability model for X ? X 0 1 2 3 P ( X ) 0.5 0.2 0.4 -0.1 X 0 1 2 3 P ( X ) 0.2 0.1 0.2 0.3 X 0 1 2 3 P ( X ) 0.5 0.3 0.1 0.1 X 0 1 2 3 P ( X ) 0.3 0.3 0.3 0.3