Which of the Following Is the Best Definition of a Catalyst

Which of the following is the best definition of a catalyst?

A) A catalyst is a substance that speeds up the rate of a chemical reaction till its concentration is reduced to zero.
B) A catalyst is a substance that speeds up the rate of a chemical reaction without participating in the reaction.
C) A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed during the reaction.
D) All of these are equally good definitions.