What does a system of checks and balances protect against

What was the most important role did the diaspora play in the history of southwest asia a) it established the first kindom of iseral b) it resulted in the exodus of isrealites back to canaan c) it lead to the spreading of most jew outside of isreal d) it made isreal vulnerable arab conquest

Who built the first turnpikes in the united states? a) the national government b) state governments c) private companies d) town councils

An object weighs 40n in air , weighs 20n when submerged jn water and 30n submerged in a liquid of unknown density .what is the density of the liquid?