How to identify the subject of a sentence?

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?

Why is it difficult to determine which countries belong to europe and which belong to southwest asia

Alexander stephens’ opinion on secession and compromise led to what being written? a)the kansas-nebraska act b)the missouri compromise c)the u.s. constitution d)the georgia platform