A researcher studies water clarity at the same location in a lake on the same dates during the course of a year and repeats the measurements on the same dates 5 years later. The researcher immerses a weighted disk painted black and white and measures the depth (in inches) at which it is no longer visible. The collected data is given in the table below. Complete parts (a) and (b) below.

(a) Why is it important to take the measurements on the same date?

(b) Does the evidence suggest that the clarity of the lake is improving at the a= 0.05 level of significance? Note that the normal probability plot and boxplot of the data indicate that the differences are approximately normally distributed with no outliers. Choose the conclusion below.

A. Reject Ho.

B. Do not reject Ho

Observation	Date	Initial	After five years
1	1–25	48.1	48.9
2	3–19	57.2	59.6
3	5–30	38.5	44.8
4	7–3	61.9	66.5
5	9–13	35.2	31.0
6	11–7	74.1	72.3