()是汽油的优良组分。
A、烷烃
B、环烷烃
C、芳香烃
D、烯烃
参考答案:C
Public relations practice is the deliberate, planned and sustained effort to establish and maintain mutual understanding between an organization and its public.
A.complete
B.related
C.intentional
D.active
食品添加剂不正确使用会造成对健康的危害。