You study two regions of the moon. region 1 is densely cratered. region 2 is mostly smooth, with just a few craters. what can you conclude?

I would conclude that Region 1 is an older portion of the surface than region 2. 
The amount of clatering is usually an indication of the age of a geological surface; the more craters, the older the surface, because if the surface is young there hasn't been time for many craters to form. Therefore, Earth has a relatively young surface because it has few craters. This is because the Earth is geologically active, with plate tectonics and erosion having obliterated most craters from an earlier epoch. The surface of the moon on the other hand is much older with much more clatering. Additionally, different parts of the moon exhibit different amounts of clatering and thus are of different ages. 

B