In what ways does the U. S. system of electing the legislature preserve the principle of separation of powers

An economic term that describes happiness and its hard to measure in numbers is

Researchers have found that it takes to view a mental image that is larger or covers more distance than a smaller or more compact one.

Chen's research team randomly assigned some newborns and their mothers either to a breastfeeding promotion group (where breastfeeding was encouraged, but not required) or to a normal pediatric care group (where breastfeeding was neither encouraged nor discouraged). which research method did they use?