The Harlows' study on rhesus monkeys showed that:

rhesus monkeys raised by other primate species are poorly socialized

monkeys can be adequately socialized by imitating humans

food is more important than social comfort

social comfort is more important than food

The correct answer is D. Social comfort is more important than food

Explanation:

Harry Frederick Harlow was a psychologist that mainly studied social isolation and dependency by using rhesus monkeys mothers and their babies, but also surrogate mothers created with objects. These experiments were mainly controversial but lead to important findings, indeed due to Harlow experiments it was found social interaction was key for the development of infant monkeys as by isolating them or using only surrogate mothers they show issues in the development and the ability to socialize; additionally, Harlow found social comfort provided by the monkey mother was one of the most important elements in socialization and development of the infant monkey and that this element was more important than food and other elements for the monkey as the monkeys preferred to have social comfort over food. Therefore, one of the aspect Harlow's study on monkeys showed was that social comfort is more important than food.