The most appropriate meaning of the idiom "in a nutshell" is >Very briefly.<
This idiom means to give a brief summary of something. It is often used when someone is trying to explain something complex or difficult in a way that is easy to understand. The idiom comes from the fact that a nutshell is a small container that can hold a lot of information.
The other options are not correct.
- Extremely pale does not mean "in a nutshell."
- Under protection does not mean "in a nutshell."
- Without delay does not mean "in a nutshell."
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