What Is True About Research Designs Used by Developmentalists

What is true about research designs used by developmentalists?

A) Researchers usually rely on one study or method to reach conclusions.
B) Researchers prefer to find converging evidence from as many different kinds of studies as possible.
C) These days,researchers use experimental research designs because correlational designs have been found to have too many weaknesses.
D) Usually one investigation can definitively answer a question asked by a researcher.