Explain the difference between a fixed and a variable cost. How do these concepts change as the

Question:

Explain the difference between a fixed and a variable cost. How do these concepts change as the time horizon lengthens? In other words, are the same things fixed over a 5-year planning period that are fixed in a typical 1-year period? What about a 10-year period? What's the relevant period when we're talking about operating leverage?