Answer:
a) All the phones produced during the day in question.
Explanation:
In statistics, the Population is all the objects with the same characteristics in which we have an interest in doing an experiment or statistical analysis. Sometimes to make it more simple, we take just a sample of the population and we do the experiments with them, and then the answers are used to all of the objects.
In this case, they want to analyze all the cellphones but they only take a few to do it. So the answer is a) All the phones produced during the day in question.