Which Activity Could Be an Example of Restoration Ecology

Which activity could be an example of restoration ecology?

A) Reintroducing wolves to an area where they formerly occurred
B) Determining the effect two mutualists have on each other's reproductive rates
C) Determining the indirect effect the removal of lions has on plants via trophic cascades
D) Introducing a novel pathogen to help control the spread of gypsy moths and eliminate native caterpillars that damage commercial timber
E) Removing wolves from a national park to restore elk populations for hunters