Given that x is a normal variable, which of the following statements is true?

a. the variable 5x is also normally distributed

b. the variable x+5 is also normally distributed

c. the variable x−5 is also normally distributed

d. all of the above statements is true

like the normal distribution, the exponential density function f(x)

a. approaches zero as x approaches infinity

b. is symmetrical

c. approaches infinity as x approaches zero

d. is bell-shaped