Which of the following could not be probability density functions for a continuous random variable? Hint: Find the area under the function f(x).

Which of the following could not be probability density functions for a continuous random variable? Hint: Find the area under the function fx). a. (x) = .25 for 0 = x = 1 O This is not a PDF. O This is a valid PDF. b. (x) = .25 for 0 = x = 4 O This is not a PDF. O This is a valid PDF. c. f(x) = xfor 0 = x = 2 O This is not a PDF. O This is a valid PDF