Which of the following command sets the Bash variable named TEST with the content FOO?

The set builtin is used to set shell options or positional parameters, not to assign named variables.

Spaces around the = sign cause Bash to interpret TEST as a command and = and "FOO" as its arguments, resulting in a command-not-found error.

var is not a Bash keyword; it is used for variable declaration in languages like JavaScript and is not recognized in Bash.

The correct Bash syntax for variable assignment is NAME=VALUE with no spaces and no keyword. TEST="FOO" directly assigns the string FOO to the variable TEST, following the shell grammar rule that any spaces around = would cause the shell to interpret TEST as a command name rather than a variable.