I would think water moves the boats
I would say D. is the right answer.
<span>Building railroads stimulated the national economy not only by improving transportation, but also by creating a huge demand for iron, wooden crossties, bridges, locomotives, freight cars, and various kinds of equipment needed to operate railroads.</span>
Ethnic groups in Rwanda. The largest ethnic groups in Rwanda are the Hutus (about 85% of the population), the Tutsis (14%), and the Twa (1%). Starting with the Tutsi feudal monarchy rule of the Tenth century, the Hutus were a subjugated social group.
I believe it's the income effect but i am not 100% sure