Concept:In tropical Africa, air transport faces low demand because tickets are costly for most people.
Explanation:Air transport is very fast, so slow speed is not a problem.
Air freight charges are usually high, not low.
Adequate space is not an issue; aircraft actually offer limited space.
In tropical Africa, many travellers cannot afford airfares.
As a result, airlines often operate with few passengers and low patronage.
Thus, low patronage is the notable problem.
Answer:D. low patronage