[单选题]
97.18: A motorist travelo9itecs6bzf bt (4 t:r 1rz01ms z6y* n)tts r c-x:/5ubbdi)dxljl 3- n400 km at 80 km/h and 400 km at 100 km/h. What is the average speed of the motorist on th3s5 ) bb6d)/*l uxljyx dcn-:tr-tinzis trip?
A. 84 km/h
B. 89 km/h
C. 90 km/h
D. 91 km/h
E. 95 km/h