It is important for children, who are the leaders of the future , to know how the govt of their country works.
Therefore, children should be taught the history of their country and how its government was formed.

Which of the following, if true, most weakens the argument above?

A. Every person who knows how the govt of a country works, knows how the govt was formed
B. Only people who know how a country's govt was formed, know how it works
C. most people who know how a country's govt was formed, know how its govt works
D. Some people who know how a country's govt works do not know how its govt was formed.
E. Some methods of teaching about the history of a country are less effective than the others

Source : Kaplan..

Am baffled!!!
Can someone help out with this? The reasoning provided by kaplan was too brief for my understanding.
Will post the OA when i get some replies . (Sorry for that)