Does money have to be involved when you talk about opportunity cost? Why or why not?

Opportunity cost is the profit lost when one alternative is selected over another. ... Opportunity cost does not necessarily involve money. It can also refer to alternative uses of time. For example, do you spend 20 hours learning a new skill, or 20 hours reading a book?

there are two main types of historical sources: primary sources and secondary sources. a primary source is something that originates from the past. it can be a chronicle, a piece of pottery, or even a piece of glacial ice that gives us climate data about the levels of atmospheric carbon one thousand years ago.