What is the relation between a material's stress and strain?
The relation between stress and strain can be observed using a stress-strain curve. This is a fundamental property of a material. The curve shows stress as a function of strain and hence shows the yield behaviour for a particular material. Observing the stress-strain curve, one can infer whether the material is ductile or brittle.
Can you explain recursion?
Let's take a look at the acronym "GNU". Full form of GNU is GNU's Not Unix. As you can see, this full form still contains GNU and hence it can further be expanded as - (GNU's Not Unix)'s Not Unix - and so on. This is recursion in the easiest possible way.
What are the advantages of a free economy?
A free market economy encourages innovation by individuals. People work with the belief that their efforts will be compensated in future. In a free economy, it is easier to get richer or poorer based on your efforts since resources are not allocated by the government.