This is my homework and i'm having some i know it looks easy but i can't decide what the answer is plz .

According to the federal regulations, which of the following studies meets the definition of research with human subjects? a study of twenty 4th grade classrooms in which researchers ask the schools to systematically vary the time of day reading is taught, and collect weekly assessments of reading comprehension for each child over a three-month period. the collection of data, by a playground designer hired by the superintendent of schools, about the physical dimensions of school playgrounds, presence of fencing, and the kinds of equipment currently provided. a feasibility study for implementing a year-round school program, focusing on economic issues such a facilities utilization and transportation costs. an analysis of aggregate data comparing statewide high school graduation rates provided by the state department of public instruction, using county tax information.

Give an example of a situation in which an individual's pursuit of economic self-interest may not benefit but instead harm the rest of society

The controlled use of fire by hominids: (a) limited the expansion of hominids into certain environments, such as dry grasslands. (b) decreased the amount of food energy available in the hominid diet. (c) contributed to geographical expansion and food production techniques in positive ways. (d) has been shown to contribute little to the digestive process of hominids.