Correct Answer: A
Explanation:
The placement of "only" in the sentence makes the sentence confusing, as it seems as if the subject were "only" one of many "third drivers" "to win ten races in one season," which doesn't make sense. The sentence only makes sense if it suggests that the driver in question was just "the third driver" ever to achieve the feat. The answer choice that correctly deploys "only" is, "He was only the third driver to win ten races in one season."