Answer: A. Word of mouth is a useless data source.
Explanation: Experimentation refers to an empirical procedure or process which is used to validate an hypothesis or establish a fact. However, experimentation requires rules which guides the process, these rules are necessary in other to avoid bias, false conclusions or inference.
According to the options given in the question above, facts used in experimentation should be traceable and reproducible. Word of the mouth is a useless data source as it usually has no empirical basis. Expert opinion or information being established by three or six sources could be considered as a fact.
