A tough outer covering, lack of leaves, and covered buds are all signs of which plant process?

dormancy

photoperiodism

abscission

photosynthesis

Plants often go into the dormant state to protect themselves from suboptimal conditions (usually harsh winters). A tough outer covering can protect the plant from freezing, the buds are covered for this same reason. The leaves fall to minimize the loss of energy since in the winter there is usually not enough sunlight to sustain the process of photosynthesis.