What is the main topic of this passage? [br] [originaltext] Those who had

Those who had seen the film at previous sessions are divided into groups studying the elements of a petroleum-free community: food, water, shelter, health and medicine, and alternate energy sources. The energy group, which includes two solar equipment installers and a re- tired engineer/physicist, will study existing alternative energy sources and determine which are possible here. Also on the list are alternate-fuel transit systems, energy waste and conservation potential, and the offerings of at least two bio-diesel suppliers. The shelter group is considering such alternate building styles and how much of the needed material can be produced locally. Group members want to know how many people will need housing in the future and how to develop new housing without jeopardizing agricultural land.  Opportunities for making existing housing more energy efficient and building shared-housing communities are also on the list. The health and medicine group is looking at incorporating alternative heating systems in the incoming hospital, social service networks, local cultivation of medicinal plants, and legal obstacles to alternative medical approaches.
     The water group wants to know the amount needed for a family of four and the possibility of salvaging more of the rainy season’s abundance.