What is the biggest problem with selecting a site for a preserve?

What is the biggest problem with selecting a site for a preserve?

A) Only lands that are not useful to human activities are available for preserves.
B) Most of the best sites are inaccessible by land transportation, so making roads to them is often prohibitively expensive.
C) Making a proper selection is difficult because currently the environmental conditions of almost any site change so quickly.
D) Keystone species are difficult to identify in potential preserve sites.
E) There is always a conflict about use of land set aside for preservation.