Final answer:
A moose exhibiting signs of instability and confusion, such as walking into trees and the 'blind staggers', is most likely a sick moose suffering from neurological issues, such as brain worm infection or toxicity from the environment.
Step-by-step explanation:
The behavior described—appearing unstable on its feet, walking into trees, and experiencing difficulty or falling down—indicates symptoms commonly associated with a moose suffering from a condition known as "the blind staggers." This condition is often observed in moose that have consumed fermented or rotten vegetation containing alcohol-producing bacteria. The fermentation process generates alcohol in the moose's digestive system, leading to symptoms akin to intoxication, resulting in impaired coordination and balance.
Therefore, the most appropriate choice based on the symptoms described would be:
1) A sick moose.