移项得：3x=1，
化系数为1得：x=13，
故选B．
Jane is high school student in the United States.
A．an 18-year-old
B．a 18-years-old
C．an 18-years-old
D．a 18-year-old
硫的去除反应与磷的去除反应均为吸热反应。（）
