From the available options, the event that could cause the movement shown in the graph is "an increase in population."
This is because an increase in population would lead to an increase in demand, as seen from the graph where demand for product X increases from 4,000 to 5,000.
However, with little or no increase in supply, this leads to an increment in the price of product X from $400 to $500.
Thus, under the same production level of commodity X, the higher the demand, the higher the price of commodity X.
Hence, in this case, it is concluded that the correct answer is option A. "an increase in population."
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