Extract the answer to the question from the following context. Question: Which state had the highest rate in the southern portion of the US for the number of adults with a high school diploma? Context: The state is among the best in pre-kindergarten education, and the National Institute for Early Education Research rated it first in the United States with regard to standards, quality, and access to pre-kindergarten education in 2004, calling it a model for early childhood schooling. High school dropout rate decreased from 3.1 to 2.5 percent between 2007 and 2008 with Oklahoma ranked among 18 other states with 3 percent or less dropout rate. In 2004, the state ranked 36th in the nation for the relative number of adults with high school diplomas, though at 85.2 percent, it had the highest rate among southern states.
A:
Oklahoma