Ten years ago the number of taxpayers in Green County was slightly greater than the number of registered voters. The number of taxpayers has doubled over the last ten years, while the number of registered voters has increased, but at a lower rate than has the number of taxpayers. Which of the following must be true in Greenspace County if the statements above are true? ['The proportion of registered voters to taxpayers has remained unchanged over the last ten years.', 'Everyone who is a registered voter is also a taxpayer.', 'The number of taxpayers is now smaller than the number of registered voters.', 'The proportion of registered voters to taxpayers has decreased over the last ten years.']