Answer:
B. "He was probably grumpy because he was older than dirt."
Explanation:
In the passage above, an idiomatic expression is used when the speaker used the phrase, 'older than dirt'. An idiom is a phrase that is not meant to be be interpreted literally with the individual words used although there are few instances where this may occur.
The term 'older than dirt' means that a person or animal is very old. It was originally coined from the dirt found at the surface of the earth, believed to have existed for thousands of years.