Doctors warned against chewing tobacco ______ (作为吸烟的替代品).

A．higher-degree-holders are surely going to make more money
B．college graduates in different majors usually get paid differently
C．a master’s degree-holder in social work will surely make more money than a bachelor’s degree-holder in computer science
D．if one wants to earn $4.4 million, he or she has to try to get a professional degree such as a doctor or lawyer