All of the following human activities threatens the everglades except
a. development.
b. agriculture.
c. preservation.
d. the introduction of new species.

The answer is c. preservation.  Three other choices could lead to the destruction of the everglades as development and agriculture could mean that you would have to clear the land in order to build something new.  Introduction of new species would upset the balance of the ecosystem in that area.

according to classical republican political theory, which democratic republics would function best?

a.   small republics, with people who had similar interests

b.   large republics, with people who had competing interests

c.   republics made up entirely of landowners

d.   republics made up entirely of servants

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.