Final answer:
The destruction of the windmill is the act that destroys the symbol of the animals' work but unites them in George Orwell's 'Animal Farm'.
Step-by-step explanation:
The act that destroys the symbol of all the animals' work but unites the animals again in Animal Farm is (A) The destruction of the windmill. The windmill was a significant symbol of the animals' collective effort and the possibility of a better future. Its destruction was not only a physical setback but also a demoralizing blow to the spirit of the animals. Despite this, the event brought the animals together once more, united in their resolve to rebuild the windmill, representing their resilience and shared purpose.