Detailed Instructions: 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.
Q: Question: How many members were in the band that Elf opened for? Passage:Though his parents were from Cortland, New York, Dio was born in Portsmouth, New Hampshire, where his family resided for his father's service in the U.S. Army during World War II; they soon returned to Cortland. Dio's music career began there in 1957 as part of the Vegas Kings (later Ronnie and the Rumblers). In 1967, he formed the rock band Elf, which became a regular opening act for Deep Purple. In 1975, Deep Purple guitarist Ritchie Blackmore founded the band Rainbow and hired Dio to be his lead singer where the band released three studio albums. Dio quickly emerged as one of heavy rock's pre-eminent vocalists. In 1979, Dio joined Black Sabbath as lead singer. He appeared on three studio albums with the band which met with success: Heaven & Hell (1980) and Mob Rules (1981) and Dehumanizer (1992). In 1982, he left the band to pursue a solo career with two albums certified platinum by RIAA. In 2006, he founded the band Heaven & Hell with ex-bandmate Tony Iommi. Dio was diagnosed with stomach cancer in 2009, from which he died the following year.
 Links: a. Cortland, New York b. Deep Purple c. Black Sabbath d. Recording Industry Association of America
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
b