Option D: During the period from 1st April to 1st September, at no time was the actual progress more than the expected progress.
The statement in Option D is incorrect because it suggests that the actual progress never exceeded the expected progress during the specified period. However, upon analyzing the graph, there might be instances where the actual progress line surpasses the expected progress line, indicating that the actual work done was more than anticipated at certain points. This contradicts the statement, making it the incorrect option. The other options accurately describe the relationship between actual and expected progress as depicted in the graph.