The 2001 census showed a sharp fall in the litreacy rate compared to 1991, but an increase in the litreacy rate by 2006 suggests that between 1991 and 2006 India progressed in terms of litreacy rate.
Which of the following statements, if true, best refutes the above argument?

The argument is that India made up for the loss incurred in literacy rate from 1991 to 2001 by improving in the 5 year span from 2001 to 2006. 
This can be refuted if it can be proven that the progress made in 2001 to 2006 was not good enough in amount to cover the losses incurred in the previous 10 year period. So even if India improved in 2001-06, the improvement might have been marginal and hardly substantial.

This is given to us by option D. Hence, the answer.