Final answer:
The three basic approaches used in modern ecological research are Experimental, Observational, and Theoretical, each involving distinct methods like controlled experiments, natural observations, and mathematical modeling.
Step-by-step explanation:
The three basic approaches that scientists use to conduct modern ecological research are A) Experimental, observational, and theoretical research. Experimental research involves conducting controlled experiments to test hypotheses under specific conditions. Observational research is about making observations in natural settings without manipulating the environment, thus it encompasses an array of studies including long-term ecological monitoring and wildlife surveys. Theoretical research involves the development and use of mathematical models to simulate ecological processes and interactions, and it helps in the prediction of future environmental conditions and management outcomes.