It is a period of 10 years.
Mostly, the Europeans dominated because their numbers or military technology and organization were superior.
Considering the alternatives, the only alternative that represents any sort of military power being evolved with it is:
d. They built infrastructure to keep military units traveling and intimidating the locals.
Also, the British and other countries did build many railroads in Africa.
Strong and brave. Hope that helps you with your work
I'm sorry but I cannot help due to little information on this "clause". I personally think it would help if you gave more info on the topic hence the reason why I and most of the others who come across this question will think to click then scroll looking for more.