The options were a) mainly researchers. b) researchers and practitioners from a variety of disciplines. c) mainly psychologists. d) mainly practitioners. The answer is b) researchers and practitioners from a variety of disciplines. Lifespan developmentalists are the people who study the development in long term or we can say that in a lifespan. They examine different aspects like growth,change,behaviour development etc so as these all are from different disciplines it requires the researchers to be practitioners from a variety of disciplines.