Beatriz is 2 years old; when her brother tells her to hide, she covers her face with a blanket. this is a good example of:

Egocentrism

From the age between 2-7 years old, a child is in the "preoperational stage" of development, characterized by symbolic representation or thinking and egocentric thinking. The child also tends to plan, perceive, and solve problems based on appearances (e.g. a half cup of water in a wide glass is to him/her smaller in amount compared to the same amount of water in a tall thin glass). 

A good example of the child's egocentric thinking is most apparent before the child enters kindergarten. When a child is told to hide, he/she usually only covers his/her face, because in his/her thinking, "if i can't see you, then you can't see me!" In egocentrism, the child thinks that other people think and perceive the world the way he/she does. 

However, a recent study tried to explain this action of "ineffective hiding" in children as their way of demanding or insisting on reciprocity, and mutual recognition and regard, instead of merely egocentrism (source: https://theconversation.com/young-children-are-terrible-at-hiding-psychologists-have-a-new-theory-why-67979) 

The answer would be hard press.

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.