4... this is the one which makes most sense
Answer:
experimental research
Explanation:
According to my study on different research methods, I can say that based on the information provided within the question this study is an example of an experimental research. This type of approach in which one or more variables are manipulated to determine their effect on a dependent variable. Which in this situation the variables being manipulated are the type of activities that the children are subjected to, while the dependent variable that is being affected by these activities are the children's performance.
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The third and fourth options. Flatter, and Caution! :)
The Singer Solution(everyone donates all their spending money to charity, would cause economic collapse in a consumerist society)
Communism(no incentive to work hard when everyone is uniformly rewarded regardless of production)