Why do real gases not behave exactly like ideal gases?

real gases are always hotter than ideal gases.
real gas particles have significant volume.
real gas particles have perfectly elastic collisions.
real gas particles are smaller than ideal gas particles.
real gas particles have more complex interactions than ideal gas particles.

there are more than one

An engineer decides to use a slightly weaker material rather than a stronger material, since she knows that the stronger material can break suddenly. this is an example of what? a choosing a material that will show warning before it fails b using composite materials that combine strength c using a material for multiple applications d using design techniques that increase efficiency and reduce cost