Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

Which group of the 1970's featured Tony Iommi on guitar, Geezer Butler on bass and Bill Ward on drums?
geezer butler

Which American actor and singer has joined Amanda Holden as one of the judges on the current series of 'Britain's Got Talent'?
britain's got talent

What band is led by singer Axl Rose?

axl rose