the ikaros spacecraft, launched in 2010, was designed to test the feasibility of solar sails for spacecraft propulsion. these large, ultralight sails are pushed on by the force of light from the sun, so the spacecraft doesn't need to carry any fuel. the force on ikaros's sails was measured to be 1.12 mn.

The correct answer is b, social stratification is needed for a society to exist. marxist theory regarding social stratification is that due to the differing economic capacities among people in society, a natural separation occurs between those that own the means of production and those that sell their labour in the production chain.