Which of the following characters can be combined with a separator string in order to read from the current input source until the separator string, which is on a separate line and without any…

The `<<` shell operator signifies a 'here document' or 'heredoc', which reads input from the current source until a line containing only the specified separator string (often called a 'delimiter' or 'terminator') is found. This is commonly used to provide multiline input to commands or scripts.

`<|` is not a standard shell redirection or special character combination for input in this context.

`!<` is not a standard shell redirection or special character combination for input in this context; `!` is typically used for history expansion or negation.

`&<` is not a standard shell redirection or special character combination for input in this context; `&` is used for backgrounding commands or combining file descriptors.