Which action is most likely to stop succession and make an ecosystem less stable?
O A. Using fewer pesticides in gardens
B. Using less fertilizer in gardens
C. Planting a variety of native species in gardens
D. Planting nonnative species in gardens

The answer is D.  Because planting nonnative species is bad for the area because the plants that normally grow there have to compete with that new species then.  

D. Planting nonnative species in gardens.

Explanation:

Planting nonnative species in gardens are bad for your garden. The nonnatives can steal most to all of your native plants food and they can attack your native plants and kill them.