Final answer:
John Tower (option D) was the first Texas Republican elected in a statewide vote in the last half of the 20th century. He was elected to the U.S. Senate in 1961. The Long Expedition established the Republic of Texas, a short-lived republic.
Step-by-step explanation:
The first Texas Republican elected in a statewide vote in the last half of the 20th century was D. John Tower. He was elected to the United States Senate in 1961, making history as the first Republican senator from Texas since Reconstruction. John Tower's election was a significant milestone for the Republican Party in Texas, which had been dominated by the Democratic Party for decades.
Regarding the other choice offered in the question, the Long Expedition established a short-lived republic in Texas known as B. the Republic of Texas. This is not to be confused with the Republic of Texas that existed from 1836 to 1846, which was established following Texas' independence from Mexico.