My dad always says, time is money .
a. metaphor
b. irony
c. pun
d. idiom

The phrase, "Time is Money", is a metaphor. So A (: A metaphor is a direct comparison of one thing to another. Another example could be, "The kids at school are all brains." This doesn't mean that the kids at school are literally walking, talking, brains. It is a figure of speech to say that the kids at school are always thinking or the kids at school are smart. 

Conclusion is the answer