The Changing Ecology of Swamps Has Been the Subject of Much

The changing ecology of swamps has been the subject of much environmental research. One water-quality parameter of concern is the total phosphorous level. Suppose that the Ministry of the Environment makes 15 measurements in one area of the swamp, yielding a mean level of total phosphorus of 12.3 parts per billion (ppb) and a standard deviation of 5.4 ppb. The Ministry wants to test whether the data support the conclusion that the mean level is less than 15 ppb. Assume measurements are normally distributed.
-How would you define the rejection region for this test at ? = .05?

A) t < -1.761
B) t > 1.761
C) t > 2.492
D) t > 3.646 and t < -3.646
E) t > 3.787