"centro" to an English national means the "town centre" but this was marked wrong by DL. I must say I am beginning to find this hearts thing demotivating rather than motivating. Seriously thinking of going over to Fluenz or Babbel, even though you have to pay for these.
I think the secret is to not take it too seriously. I agree that it is annoying to lose a heart especially near the end of a lesson but it's not worth getting too worked up about. The 'game' approach used by DL doesn't do anything for me but the site is good.