What Is the Biggest Problem with Selecting a Site for a Reserve

Multiple Choice

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

A) Making a proper selection is difficult because currently the environmental conditions of almost any site can change quickly.
B) Keystone species are difficult to identify in potential reserve sites.
C) Only lands that are not useful to human activities are available for reserves.
D) Most of the best sites are inaccessible by land transportation, so making roads to them is often prohibitively expensive.