Answer: b. The sample should be chosen at random so that it is fair.
Step-by-step explanation:
One of the most important things when selecting a sample is that the sample must be totally random if the sample is not random (for example, selecting only the youngest people in a group or things like that) there is a high probability that the sample will be biassed towards something, so the study may not be really accurate for all the population.
The correct option is b. The sample should be chosen at random so that it is fair.