Definition: In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.
Input: Question: Where does the body of water where Dr. Nelson G. Blalock established an agricultural operation originate? Passage:The community was named for the farm of Dr. Nelson G. Blalock, a Civil War veteran who had pioneered in the Walla Walla area. He established an agricultural operation of several thousand acres on the flat land here along the Columbia River. The area was first settled in 1879, and Blalock post office was established in 1881. The town was platted in 1881 by the Blalock Wheat Growing Company. The first two buildings, a railroad station and a warehouse, were built by A. J. McLellan, OR&N superintendent of the construction of bridges and buildings. By 1884, the community was shipping wheat and there were daily stagecoaches to Heppner; the population was 50. People and businesses listed in the Polk Directory at that time included two clergymen, a saloon, a wagonmaker, a ferryman, a hotel, a general store, a lawyer, and a dealer in lumber, coal, and feed. In 1904, the town handled about 750,000 bushels of wheat. By 1905, the town had two grain warehouses, a hotel, a general store, a livery and stage stable, a real estate office and an agricultural implement factory. In 1940, Blalock had a population of 19. The post office closed in 1959. In 1968, the community was inundated by the backwaters from the John Day Dam.
Links: a. Columbia River b. General store c. Walla Walla, Washington d. Columbia River
Output:
a