In the context of birth order, research indicates that firstborn children are than later-born children.

The correct answer to this open question is the following.

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In the context of birth order, research indicates that firstborn children are more achievement-oriented than later-born children.

Researchers have studied this topic and say that firstborn boys and girls are high achievers that like to receive approval from their parents. These children are reliable, cautious, and controlling. Because they are the only child in the family, they caught all the attention and time of the parents. This allows the children to receive more information that makes them be more intelligent than other children.

the answer to this question is d