______ do not operate according to published timetable, nor are they advertised or promoted by the airlines themselves.
A.Air taxi services
B.Charter services
C.Scheduled services
D.Trunk route services
正确答案是B
______ do not operate according to published timetable, nor are they advertised or promoted by the airlines themselves.
A.Air taxi services
B.Charter services
C.Scheduled services
D.Trunk route services
正确答案是B