JAMB Geography 2012 Paper

Concept:The Earth's crust is composed mainly of oxygen and silicon, with significant amounts of aluminium.Explanation:The Earth's crust is sometimes called the sial layer because it is rich in silica ($\mathrm{SiO}_2$) and alumina ($\mathrm{Al}_2\mathrm{O}_3$).Silicon and aluminium are therefore the characteristic non-oxygen elements of the crust.Thus, the essential composition is silica and aluminium.Answer:B. silica and aluminium