Level 12 books feature greater use of literary language and more unusual and challenging vocabulary. Play scripts also feature from Level 12. Non-fiction titles contain longer, more formal sentences and a wide range of unfamiliar terms. Sentences become longer with greater use of conjunctions and relative clauses. Grammatical vowel endings are more evident to encourage fluent reading and to provide familiarity with some higher-level features of written Arabic. Hot-air balloons, gliders, solar-powered planes ... Climb board and find out about the world of aircraft. This fascinating history of human flight follows the incredible technological advances that allowed what was once an impossible dream to become a matter of routine for millions.