The correct answer is B) financial assistance.
The US government gives financial assistance to students who study certain fields in college and graduate school to increase the supply of educated workers in these fields.
The government of the United States knows the necessities that need to be covered in some industries or areas of production. Sometimes, for any particular reasons, these areas need more workers in determined specialty fields. It could be engineering, mathematics, or sciene. That is why, as a stimulus, the government gives financial assistance to attract more students to follow these careers.