"Most attention" is ambiguous, particularly when some of the options are phrased as proactive and others reactive/preventative. Do you man funding? Public awareness? Plus there some issues might be incredibly important but require relatively little "attention" to solve while others might be less important but take a lot more resources to solve. I wouldn't know how to answer this question accept to say I don't think any effort should be spent on creating and deploying anti- grey goo nanotech.