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

[Q]: What is the country of origin of the cheese called caerphilly?
[A]: caerphilly cheese


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


[Q]: What SI unit (International System of Units) of measurement is defined as The amount of substance that contains an equal number of elementary entities as there are atoms in 0.012kg of the isotope carbon-12?
[A]:
amount of substance