A biologist hypothesizes that the mean life expectancy of a cockroach is 17 days. Researchers believe the true mean is less than 17 days and they plan a hypothesis test at the 10% significance level on a random sample of 80 of these cockroaches. If the alternative hypothesis is correct, for which of the following values of is the power of the test greatest?

A. = 9

B. = 10

C. = 17

D. = 20

E. = 21