Which of the following command line redirection characters instructs the shell to read from the current input source until a specific word, on a separate line and without and trailing spaces, is…

The `<<` operator is used for a 'here document' which allows multi-line input to be provided directly within a shell script or from the command line. The shell reads all subsequent lines as standard input for the command until it encounters a specified delimiter word (on its own line, without leading/trailing spaces).

`<|` is not a standard shell redirection character for here documents; `<` redirects input from a file, and `|` creates a pipe.

`!<` is not a standard shell redirection character; `!` is generally used for history expansion in Bash.

`&<<` is not a standard shell redirection character; `&` is used for file descriptor manipulation or backgrounding, not in this combination for here documents.