An army depot that overhauls ground mobile radar systems is interested in improving its processes. One problem involves troubleshooting a particular component that has a high failure rate after it has been repaired and reinstalled in the system. The shop floor supervisor believes that having standard work procedures in place will reduce the time required for troubleshooting this component. Time (in minutes) required troubleshooting this component without and with the standard work procedure is recorded for a sample of 19 employees. In order to determine if having a standard work procedure in place reduces troubleshooting time, they should use
a. a one-tailed paired t-test.
b. a two-tailed test of two independent means.
c. a one-tailed test of two independent means.
d. a two-tailed paired t-test.
e. a test of two proportions.