In 2014, slightly less than ______ of voting-age Americans showed up at the polls.

Why might even a period of prosperity bring about revolution?

A) When people move in and out of poverty, they have no hope for the future, and so see nothing to lose in rebelling. B) When things improve for the wealthy, they start imagining an even better future. No longer content with their already luxurious lot, they want improvement faster than even a growing economy can deliver. C) When things improve for the poor, they realize just how bad they've had it and their anger is unleashed. D) When things improve for the poor, people start imagining a better future, and no longer content with their lot, they want improvement faster than even a growing economy can deliver.

What are the three threats to internal validity associated with measurement?

What will be an ideal response?