The underlined word "tainted" in the first paragraph most probably means ______.

A．the harmful effects of chlorofluorocarbons on the environment
B．the necessity to ensure the environmental compatibility of new chemical substances
C．the economic feasibility of new chemical substances
D．the objective assessment of the progress in chemistry

A．There conflicts were instigated by eastern interests against western settlers.
B．These conflicts were the most serious kind of conflict in America.
C．The conflicts eventually led to openly expressed class antagonism.
D．These conflicts contained an clement of class hostility.