The scenario described with the peppered moth populations undergoing selection for light and dark moths in different environments is an example of disruptive selection. This type of selection favors individuals at both extremes of a trait distribution while selecting against the average.
The distribution curve for all peppered moths under disruptive selection would therefore have two peaks at the extremes of the graph with a dip in the middle.
So the correct response is: disruptive selection; two peaks at the extremes of the graph with a dip in the middle.