Read the Following Scenario and Answer the Question Below

Read the following scenario and answer the question below.
Many biologists and environmental educators are interested in maintaining biodiversity in urban landscapes, where preserves or reserves are scarce unless land has been set aside for them in urban planning. Nonetheless, they have discovered that making even small changes in commercial and residential landscaping can help promote biodiversity. Some of the changes that have been recommended and been successful include using native species for street trees and for decorative landscaping, reducing pesticide use on lawns and gardens, and reducing fertilizer use through composting and mulching.
Also, managers of schools, larger businesses, and residences are encouraged to increase habitat diversity by creating "landscape islands" that include larger trees surrounded by shrubs and herbaceous plants. Landscape islands ideally should include native species, mixed with exotic ornamentals at the discretion of the land owners.
-Removal of which of the following species will always result in the greatest changes in an ecological system?

A) a keystone species
B) a carnivore species
C) a competitive species
D) a producer species
E) a decomposer species