Answer: All infants
Step-by-step explanation:
In statistics,
Population is a term that is used to represent the largest group sharing similar charcteristic from the researcher's point of view.
A sample is a subset of the population.
Here, a sample is collected of infants which were subjects for the study.
Objective of study: To check if reducing body temperature for 3 days after birth improved their chances of surviving without brain damage.
Here, the population of interest is "All infants".