In the Past, the Mean Running Time for a Certain $8.4$

In the past, the mean running time for a certain type of flashlight battery has been $8.4$ hours. The manufacturer has introduced a change in the production method and wants to perform a hypothesis test to determine whether the mean running time has increased as a result. The hypotheses are:
$\begin{array} { l } H _ { 0 } : \mu = 8.4 \text { hours } \\H _ { A } : \mu > 8.4 \text { hours }\end{array}$
Explain the result of a Type II error.

A) The manufacturer will decide the mean battery life is greater than $8.4$ hours when in fact it is greater than $8.4$ hours.
B) The manufacturer will decide the mean battery life is less than $8.4$ hours when in fact it is greater than $8.4$ hours.
C) The manufacturer will decide the mean battery life is $8.4$ hours when in fact it is $8.4$ hours.
D) The manufacturer will decide the mean battery life is $8.4$ hours when in fact it is greater than $8.4$ hours.
E) The manufacturer will decide the mean battery life is greater than $8.4$ hours when in fact it is $8.4$ hours.