An expression that involves a ratio.
Work Step by Step
There are two possible options given. However, the first answer, an expression that makes sense, does not make sense as an answer. After all, if an expression does not make sense, then we would never use it at all. This would mean that all expressions would be rational, so we would not need the term "rational" to tell us that the expression is rational. Thus, we know that the second answer, an expression that involves a ratio, is correct.