the explanation

Hi, I'll take a stab at why we can prove they agree about D. D tells us that they would agree that the people of the country are worried about the present state, as shown by their nostalgia. M tells us that nostalgia is evidence that people regret the revolution, which certainly would be an issue with the current state. R, however, tells us that nostalgia is evidence they are troubled with their country, albeit for different reasons. So, we have strong reasons to think that both of them agree on D.