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13.99 kilometers is the diameter.
Divide the circumference (43.96) by 2(pi), which should give you a radius of 6.99. You should then proceed to multiplying that by 2, since radius is half of the diameter, giving you 13.99.
The correct answer is extrinsic motivation.
Extrinsic motivation refers to behavior that is driven by external rewards. In other words, the motivation to engage in a behavior arises from the outside sources because it is naturally satisfying to them. Practically, the behavior is driven by a reward given by someone or something else if the particular thing is done correctly. In this example Brenda is motivated to study more because she wants to earn an A, thus a reward for her effort of studying.
Conditioning creates the brain's pattern recognition which makes it easier or harder. Abusive conditioning makes recognizing kind/nonviolent much more difficult, etc.