part c is this investigation a controlled experiment or an observational study? explain your answer.

Brief Explanations:

A controlled experiment involves manipulating an independent variable while controlling other variables. An observational study just observes and records data without manipulation. Without details of the investigation, if there's variable - manipulation it's a controlled experiment, if just observation it's an observational study.

Answer:

Without details of the investigation, it's impossible to determine if it's a controlled experiment or an observational study. If the researchers manipulate variables while controlling others, it's a controlled experiment. If they only observe and record data without any manipulation, it's an observational study.