What keeps some people from transition to a higher category of labor?

What event helped increase Chinese immigration in the US? What are three types of pollution? What procedure requires a physician to cut down the superficial fascia? What were the descendants of black slaves and europeans called? What does the Montgomery bus boycott have to do with the civil rights movement? What are the major accomplishments of each wave of feminism? Why did people think slavery was acceptable? Non institutional correction? What did Cesar Chavez advocate to open the door to a better life? What do you call someone who supports charities to help others? Can you please tell me what human environment interactions are happening in NYC? How can household farming could reduce poverty? What is used to share public resource? Where does human sewage eventually flow? What are Angola's domestic issues? How the acquisition of materials or resources constitute a threat to the environment? Air pollution due to thermal power plant? Do you think the government should spend money promoting community cohesion? What is a person called who sleeps with both genders? What kinds of social policy initiatives might be suggested by social development perspectives?

What keeps some people from transition to a higher category of labor?