In the context of the plot diagram you provided, the events that would fit into the middle (the rising action and climax) are:
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After Gortsby loans the young man money for a hotel room, the elderly gentleman returns to the bench to look for a lost cake of soap.
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After Gortsby finds a cake of soap lying on the bench and believes that the young man left it there.
These details build tension and lead to the climax of the story, as they involve key interactions and the development of the plot.