Amarine biologist is examining the effects of oil pollution on a population of seagulls (larus canus). he is particularly interested in determining whether oil pollution reduces the number of eggs that may be hatched in each seagull nest. during one breeding season, he has counted the number of eggs present in 16 seagull nests and recorded the distance from each nest to a nearby oil refinery. which step would best enhance the data from this study and allow the researcher to reach more confident conclusions? a) data could be gathered from nesting sites near other oil pollution sources. b) the research could be expanded to include fish and other marine dwelling creatures. c) the effects of other pollutants such as air pollution could be included in the study. d) the researcher could increase the number of independent variables included in the study.