Task: Class Definition Understanding (ontology: Sciences/Biology)

Which of the following definitions best describes 'ketone'?

A. Any steroid having a ketone functional group.
B. A compound in which a carbonyl group is bonded to two carbon atoms: R2C=O (neither R may be H).
C. A ketone that is cycle. The simplest class have the formula (CH2)nCO, where n varies from 2 for cyclopropanone to the teens.
D. A ketone of general formula R(1)R(2)C=CR(3)-C(=O)R(4) (R(4) =/= H) or R(1)C#C-C(=O)R(2) (R(2) =/= H) in which the ketonic C=O function is conjugated to an unsaturated C-C bond at the alpha,beta position.

Answer: A compound in which a carbonyl group is bonded to two carbon atoms: R2C=O (neither R may be H).