Solution:
Let x represent the number of installations that each unit on the y-axis represents.
Then 9x,5x,6x,4x, and 3.5x are the number of rooftops with solar panel installations in cities A, B, C, D, and E, respectively.
Since the total number of rooftops is 27,500, it follows that 9x+5x+6x+4x+3.5x=27,500, which simplifies to 27.5x=27,500. Thus, x=1,000.
Therefore, an appropriate label for the y-axis is “Number of installations (in thousands).”
Choices A, B, and D are incorrect and may result from errors when setting up and calculating the units for the y-axis.
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