If you travel to Sanya, Hainan, the fastest mode of transportation is () A. Railway B. Highway C. Waterway D. Aviation.

Understand the characteristics of various modes of transportation: road transportation is flexible, door-to-door and suitable for short-distance transportation; Air transportation is fast, but small in size, suitable for long-distance transportation that is urgently needed; Railway transportation is fast and large, which is suitable for long-distance transportation with large volume; The water transport volume is large, but the speed is slow, which is limited by the region and suitable for long-distance transportation with large volume between two seaports; Pipeline transportation is underground and generally suitable for long-distance transportation of oil, natural gas and water. Dalian is far from Sanya, and the fastest way is by air.

Therefore, choose: d.