Increasing participation by a Win-Win mechanism

For now, random sentences are given to the user to spell, the user is doing so just to help the community, I may feel that I’m wasting my time a little because these sentences don’t have any sense to me. I suggest providing the user the possibility to select the domain of the sentences he is going to spell. For example, maybe I’m interested in geography, and maybe spelling geography-related sentences will be more beneficial for me, so I may spend more time reading the sentences.