Concept:Sustainable development is development that meets present needs without spoiling the ability of future generations to meet theirs. It needs a calm environment in which plans can be carried out over many years.Solution:Peace and stability allow investment, production, trade and long-term planning to go on without interruption.Untapped (unused) natural resources do not by themselves bring development; unskilled labour lowers productivity; university graduates help only when the country is peaceful enough to use them.So sustainable development depends on peace and stability.Answer:Option A (peace and stability)