Athletes performing in bright sunlight often smear black eye grease under their eyes to reduce glare. Does eye grease work? In one study, 16 student subjects took a test of sensitivity to contrast after 3 hours facing into bright sun, both with and without eye grease. This is a matched pairs design.
Here are the differences in sensitivity, with eye grease minus without eye grease:

0.07 0.64 -0.12 -0.5 -0.18 -0.14 -0.16 -0.03

0.05 0.02 0.43 0.24 -0.11 0.28 0.05 0.29

We want to know whether eye grease increases sensitivity on the average.

1) What are the null and alternative hypotheses?

A. H0 : ? = 0 ; Ha : ? ? 0
B. H0 : ? = 0 ; Ha : ? > 0
C. H0 : ? = 0 ; Ha : ? < 0
D. H0 : ? = 0.10125 ; Ha : ? > 0.10125

2) Say in words what mean ? your hypotheses concern.

A.? is the mean sensitivity in the population.
B.? is the mean sensitivity difference in the sample.
C.? is the mean sensitivity difference in the population.
D.? is the average of mean sensitivity differences in many SRS's of size 16 from the population.