Which level of organization does the complete skeleton of a mouse belong to

The complete skeleton of mouse belongs to the ORGAN SYSTEM LEVEL OF ORGANISATION.
The organ system level of organisation is made up of different cells, tissues and organs which work together in the living organisms to create a particular system. The organ system organisation is the highest level of organisation in living organisms. The complete skeleton of a mouse is described as its skeletal system.

D. pray lands grasslands swamps

Ithink its because more have died recently than in the past.