Answer:
The true sentence about the sample is B. It is not a valid sample because it is not a random sample of the population.
Step-by-step explanation:
The concept of random sample involves that the sample have to be representative and with the minimum bias. If the researcher wants to arrive to a conclusion about the population, eight individuals are not enough and he needs a method to select from his subsample (all individuals who respond the advertisement in a given period of time), individuals that will finally participate .