You Enjoy Learning About History by Traveling Throughout North America

You enjoy learning about history by traveling throughout North America studying gravestones.You notice that gravestones from 1900 and earlier usually host many types of lichens.But in one cemetery,lichens are entirely absent,even from old gravestones.Given what is known about lichens,the cemetery without lichens probably

A) is close to a source of air pollution.
B) gets a great deal of rain,which favors the growth of competing bacteria.
C) has an unusually dry climate.
D) is subject to extremely cold winter temperatures.