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fn: In Rust, the "fn" keyword is used to define functions. It is the standard way to declare functions in Rust code.

A custom data structure: A "struct" in Rust is used to define a custom data structure with named fields. It's a fundamental building block for creating complex data types.

let: In Rust, the "let" keyword is used to declare and bind a new variable. It is the standard way to introduce variables in Rust.

Memory safety: The primary goal of Rust programming is to ensure memory safety without sacrificing performance. This means preventing common programming errors like null pointer dereferences and buffer overflows.

Pattern matching: The "match" expression in Rust is primarily used for pattern matching. It allows you to match values against patterns and execute code based on those matches, making it a versatile feature for control flow and data manipulation.

string: String is not a primitive data type in Rust; it's a collection of characters and is managed as a part of the standard library.

All of the above: Rust's ownership system aims to prevent a range of common programming issues, including buffer overflows, memory leaks, and data races, to ensure program reliability and safety.

Referencing a value: "Borrowing" in Rust allows you to create references to values without transferring ownership. It's a key concept for working with data in a safe and controlled manner.

Define a custom type: An "enum" in Rust is used to define a custom type with a finite set of named values (variants). It's often used for creating types that represent multiple possibilities, making code more expressive and safe.