For this case, we have that by definition, the difference is represented by the mathematical sign "-", also called signs of subtraction or sign of subtraction.
Then we discard options A and B.
We have the option C:
![6 + x-9](https://img.qammunity.org/2020/formulas/mathematics/middle-school/esj0qgz2iefoz9hiig3wxm93bdkkktobry.png)
It contains a sign of addition and also refers to three terms.
Finally, in the last option, we have a difference of two terms.
is the first term
is the second term
ANswer:
Option D