The correct option is C He was elected to the Tennessee House of Representatives.
"he married Sarah Childress, the daughter of a prominent planter and merchant from Murfreesboro." - this sentence does not exactly fit with the context of the passage- the passage talks about the professional life of Polk, so mentioning his personal life does not fit. This eliminates option A and B. In the sequence of events Polk was first elected to the Tennessee House of Representatives and after his term was up, he went to serve as the governor of Tennessee. This eliminates C. Option D best fits the context and is the correct answer.