It is simply asking you which one increased the most from its last interval.
Answer : 4 | 2006 - 2012
From 1898 - 1971 it increased by 5
1971 - 1985 increased by 8
1985 - 2006 it increases by 10
2006 - 2012 it increased by 11 ( this is the answer because it increased the most compared to the others)
