From the provided study descriptions, state whether the study was experimental or observational.
a) A researcher is carrying out a study on the reliability of four different solar systems. She has sixteen 3 kW properties and plans to randomly assign each to one of the four treatment groups.
b) To examine first graders’ hours of screen time a week, researchers prepared a questionnaire to be filled by parents.
c) Is the perspective of business owners in Chattanooga, Tennessee, as a place of business, independent of their perspective of its affordability?
To answer this question, the survey answers from 2172 participants will be used.
d) To test new drone propellers, 20 unmanned aircrafts were randomly assigned to fly with either the new propellers or the traditional ones. Then their average speed was estimated.