Which of the following could not be probability density functions for a continuous random variable? Explain. Hint: Find the area under the function f(x). a. f(x) = .25 for 0 ≤ x ≤ 1 b. f(x) = .25 for...

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

a. f(x) = .25 for 0 ≤ x ≤ 1

b. f(x) = .25 for 0 ≤ x ≤ 4

c. f(x) = x for 0 ≤ x ≤ 2