The cell membrane is a structure that separates the cell from its environment. Identify an object or molecule that cannot pass through the cell membrane.
Explain why preventing the free passage of this object or molecule helps the cell.

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?