Answer: 3. It suggests that the heat has real power to change its environment.
Explanation: Personification is a figure of speech that consists in giving human characteristics to nonhuman objects, or also it can be describing an abstract concept using human features. In the poem "Heat" by H. D. the author uses the personification of heat describing how it blunts the fruit as if it were a human being with the capacity to shape objects, and this personification suggests that the heat has real power to change its environment.