Select the most appropriate idiom that can substitute the underlined segment in the given sentence.
We need to make sure that criminals like these get more from the authorities than a very mild punishment.

The correct option is a slap on the wrist.

Explanation:
The idiom "a slap on the wrist" refers to a very mild, lenient, or light punishment given to someone who has committed a crime or fault.
In the given sentence, replacing the underlined phrase "very mild punishment" with "a slap on the wrist" maintains the original meaning while adding idiomatic expression: "We need to make sure that criminals like these get more from the authorities than a slap on the wrist."

Meanings of the other options:
• An axe to grind: To have a private reason or personal grievance for doing something.
• A blessing in disguise: Something that seems bad or unfortunate at first, but turns out to have a good result later.
• A taste of their own medicine: Sample of the same unpleasant treatment that one has previously given to others.