Over the last 10 years, there has been a dramatic increase in the number of people over the age of 65 living in this region. This is evident from the fact that during this time the average age of people living in this region has increased from approximately 52 to 57 years. Which one of the following, if true, would most strengthen the argument? ['The number of people in the region under the age of 18 has increased over the last 10 years.', 'The birth rate for the region decreased significantly over the last 10 years.', 'The total number of people living in the region has decreased over the last 10 years.', 'The average age for people in the region is higher than that for people in surrounding regions.']