The information provided indicates that there is a breeze blowing from the west over the town of Dansbury, and in the summer, there are often showers in the afternoon. Given these conditions, it is most likely that there is a source of moisture to the west that contributes to the showers.
Among the options provided:
A. a mountain - Mountains can attract moisture and lead to rainfall, especially if they are part of a larger range that captures humid air.
B. a desert - Deserts are typically dry and would not likely contribute to afternoon showers.
C. a valley - Valleys do not specifically indicate a source of moisture and could be dry as well.
D. a lake - Lakes are significant sources of moisture and can lead to increased humidity and precipitation, especially in summer.
Considering these possibilities, the most likely answer is D. a lake, as it would provide the necessary moisture to create the afternoon showers described.