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.
Input: Question: How long had Les Paul guitars been made by Gibson? Passage:Old Black is a 1953 Gibson Les Paul Goldtop, painted black and customized considerably. After the guitar had been left at a guitar repair store, the original P-90 bridge pickup was replaced with a Gretsch Dynasonic single-coil pickup. Eventually, a mini humbucker pickup from a Gibson Firebird guitar replaced the Dynasonic. The neck pickup has always been the original P-90 pickup, but it is now covered by a hand fitted aluminum P-90 cover, replacing the original white plastic cover. The guitar was roughly resprayed to jet black, and received a new Tune-o-matic bridge (not available when the guitar was produced) and a B-7 model Bigsby vibrato tailpiece. It would presumably also have had a white plastic pickguard at some point, as was standard on 1953 Goldtops. Old Black is notable for its metal hardware, including aluminum backing plates. The pick guard is chrome-on-brass/bronze. The tuners have been replaced with Schaller M-6 tuning keys, and the rest of the hardware is mostly nickel-plated. The headstock displays a partially painted-over mother-of-pearl inlay, sometimes referred to as a "wheat stack", rather than the typical silk screened "Les Paul Model" logo, along with single-ply binding around the headstock, although the binding has now fallen off.
Links: a. Gibson b. P-90 c. Nacre d. Bigsby vibrato tailpiece
Output:
a