You're writing a Terraform configuration that needs to read input from a local file called id_rsa.pub. Which built-in Terraform function can you use to import the file's contents as a string?

fileset() returns a set of file paths matching a glob pattern within a directory, not the contents of a single file.

filebase64() reads a file and returns its contents encoded as a Base64 string, not a plain string.

templatefile() renders a template file by substituting variable expressions and requires a variables map as a second argument; it is not used for simple file import.

The file() function reads the contents of a file at the given path and returns it as a string. It is the standard Terraform built-in for importing raw file content - such as an SSH public key - directly into a resource argument like aws_key_pair.public_key.