system of pulley graphic and classes of levers, probably 2nd grade or above.
10 Scariest Theories Known to Man
24 Essential Chess Tips That Will Make You Understand The Game Better.. GREAT LIST ie,, about ROOKS - Rooks belong on open files. Doubling the rooks almost triples their power. Two rooks are usually better than a queen.
NYC chess board
The Psychology Of Music [Pic] ~ Would Music Therapy help a person with Brain Bleed / Damage / Injury ??
Een overzicht van de verschillende leertheorieën (infografiek) | X, Y of Einstein?