Which of the following are techniques that companies use to influence consumer demand for their goods and services '

When zhang qin went to explore west, he brought back stories of

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?

What does the author describe in this passage