If many firms producing similar headphones enter the market, the demand for the headphones produced by existing firms will most likely ______.

All the goods and services we produce are ____________ .

a. expensive. b. scarce. c. recyclable. d. efficiently produced.

Physical objects are rival in the sense that ________

A) they are necessarily in opposition to one another B) they are nontrivial C) when they are used in one activity, they cannot be used in another D) some countries possess natural resources, e.g. oil, while some do not