Which of the following symbols represents the null hypothesis?

A) H₁
B) _
C) X₁
D) H₀

In a Poisson probability problem, the rate of errors is one every two hours.To find the probability of three defects in four hours,

A) μ = 1, x = 4.
B) μ = 2, x = 3.
C) μ = 3, x = 2.
D) μ = 3, x = 6.