Traditional vegetation in Oklahoma's prairies include bluestem, Indian grass, and post oak-blackjack trees.
A. Piñon pine-juniper trees: These trees are more commonly found in higher elevations and drier environments, not in the typical prairie regions of Oklahoma.
B. Mesquite trees, on the other hand, are well-adapted to the dry climate and open grasslands of Oklahoma and are a prevalent component of the traditional prairie ecosystem.
C. Post oak-blackjack trees: These trees are more characteristic of the eastern woodlands in Oklahoma, not the central prairie grasslands.
D. Oak-hickory trees: While oak trees are present in Oklahoma, the specific combination of oak and hickory is more typical of the eastern forests and not the dominant vegetation in the prairies.
Therefore, C. post oak-blackjack trees is the most accurate choice for traditional vegetation in Oklahoma's prairies.