21. The true average diameter of ball bearings of a certain type is supposed to be .5 in. A one-sample t test will be carried out to see whether this is the case. What conclusion is appropriate in each of the following situations?

a. n
13, t
1.6, 
.05

b. n
13, t
1.6, 
.05

c. n
25, t
2.6, 
.01

d. n
25, t
3.9