Answer:
B. 40
Explanation:
What do you understand by sample size; a sample size is a little portion of a large number we which to investigate. Imagine we wanted to know the electricity consumption of people in a town of 200million people sometimes we could do that be investigating that of 50million especially when you know the conditions would be no different from others. In this sense the sample size is 50 million because that's the one we are investigating.
Similarly our concern of interest for investigation is 40, so that's the sample size.