Given the task definition and input, reply with output. 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.

Question: Which original member of Jethro Tull was the youngest? Passage:Jethro Tull are an English progressive rock band from Blackpool. Formed in December 1967, the group originally included vocalist and flautist Ian Anderson, guitarist and backing vocalist Mick Abrahams, bassist Glenn Cornick and drummer Clive Bunker. After contributing to the band's debut album This Was, Abrahams left Jethro Tull in December 1968, citing disagreements with the band's "basic policies, both musically and otherwise". He was replaced before the end of the year by Martin Barre, after rehearsals and stand-in performances by David O'List and Tony Iommi. Keyboardist John Evan was added to the band's lineup in April 1970, after contributing to Benefit as a guest performer. By the end of the year, Cornick had left the band due to "musical differences", with Jeffrey Hammond-Hammond taking his place. Anderson was left as the sole original member of the group by May 1971, when Bunker also left due to their heavy touring schedule. He was replaced by Barriemore Barlow.
Links: a. Tony Iommi b. Jeffrey Hammond c. Barriemore Barlow d. Ian Anderson
d