Sentence:  Before the independence of India the books of Dr P. K. Yadav presented a fundamental challenge to the accepted ideas of race relations that, two <WSD>generations</WSD> later, will be true of the writings of the radical writers of the 1970s. 
Meaning of the word marked with <WSD> tags:  The average amount of time needed for children to grow up and have children of their own, generally considered to be a period of around thirty years, used as a measure of time. (from 17th c.)