What is the purpose of a lanyard attached to an engine cut-off switch?

As of 2013, the world’s total population was about

Americans often refer to a country that is not the united states as a

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?