State the conclusion based on the results of the test. the standard deviationstandard deviation inin the pressure required to open a certain valve is known to be sigma equals 1.3 psi.σ=1.3 psi. due to changes in the manufacturing process, the quality-control manager feels that the pressurepressure variabilityvariability has changedchanged. the null hypothesis was rejected. choose the correct answer below. a. there is not sufficient evidence that the mean of the pressure required to open a certain valve has not changed. b. there is sufficient evidence that the mean of the pressure required to open a certain valve has changed. c. the mean of the pressure has not changed. d. the mean of the pressure has changed. e. there is sufficient evidence that the mean of the pressure required to open a certain valve has not changed. f. there is not sufficient evidence that the mean of the pressure required to open a certain valve has changed.