Final answer:
The three conditions needed for a tree to become diseased are susceptibility to disease, changing environmental conditions, and competition for nutrients.
Step-by-step explanation:
One of the three conditions needed for a tree to become diseased is susceptibility to disease. However, this is not the only condition required for a tree to become diseased. The other two conditions are changing environmental conditions and competition for nutrients. These factors, along with genetics and environmental conditions, play a role in determining the survival of a tree.
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