Answer:
D. All the phones produced during the day in question
Explanation:
Population of interest is the population that conclusions are made for. The population can be objects, people, or measurements.
A sample is drawm from this population and tested for a particular characteristic. The result is now used to draw conclusions about the population of interest.
On this case the population of interest is all the phones produced in a day, the sample is the 50 phones selected for testing.
The characteristic tested is defects less than 0.05%. If the sample shows that defects are less than 0.05% then it is concluded that the population is okay.