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Huge curtains of green and red light flickered and danced across the northern skies , whilst the more stunning displays filled the whole sky , from horizon to horizon , with green and red beams forming a giant umbrella of light . Zinc improves growth and enhances the body 's ability to respond to infection , and vitamin A plays an essential role in the immune response and is believed to be necessary for host resistance to malaria . The psychometric properties provide information regarding the reliability of the various groups of items , as well as a difficulty index ( percent of patients who scored this item correctly ) , and an item to group total correlation for each item . This exemption from natural gas tax for hydrocarbons produced from a Texas experimental research and recovery well only applies to gas wells that have been accepted by the Texas Railroad Commission into the Texas Experimental Research and Recovery Activity ( TERRA ) . The ensemble cast and a multi-threaded plot ( signature elements of Brunner 's style ) weave together in a way that reinforces the novel 's thematic movement from isolation to unification .