Analyzing the intervals during the months from June to December based on the points provided:
- June: 0.2 inches
- July: 0.45 inches
- August: 0.55 inches
- September: 0.7 inches
- October: 1.6 inches
- November: 2.4 inches
- December: 3.2 inches
From June to October, the average rainfall increases from 0.2 inches in June to 1.6 inches in October. Then, it continues to increase from October to December, reaching 3.2 inches in December.
Thus, the overall trend from June to December is an increase in average rainfall.
Therefore, the correct response is:
the average rainfall increases.