Answer:
Explanation:
Factors:
1.-Installed time.
The installation of headstone occurs when one person died, some people die yesterday and other 70 years ago then the condition of headstones in these two cases must be very different
2.-Raw material
People use different raw material for headstones, and different materials have different behavior on the occasion of the same environmental conditions
3.-The place where the headstone was installed. Even having the same atmospheric conditions, some headstone could be supporting worse conditions than others. That means that conditions for all headstones are no the same (some of them are always clear, and others dirty, headstone will look worse and older than others)