Some archaeologists think that the Mayan cities collapsed because their lands were farmed (C) [so / too] heavily that they became worn out.<br/><br/>It 's a question I was given and I gave a worng answer. I thought it would be better to use 'so' instead of 'too'. But the answer said it's too.<br/><br/>I don't understand. Too can be acceptable in some cases, I think, but using 'so' there is worng? Why?