Which command allows you to make a shell variable visible to subshells?

A.
export $VARIABLE

B.
export VARIABLE

C.
set $VARIABLE

D.
set VARIABLE

E.
env variable

Explanation/Reference:
From the man pages:
    export [-fn] [name[=word]] …
    export -p
The supplied names are marked for automatic export to the  environment of subsequently executed commands. If the -f option is given, the names refer to functions.  If no names are given,  or if  the  -p  option  is  supplied,  a list of all names that are exported in this shell is printed.  The  -n  option  causes  the export  property  to  be  removed from each name.  If a variable name is followed by =word, the value of the variable is  set  to word.   export  returns  an  exit  status of 0 unless an invalid option is encountered, one of the names is  not  a  valid  shell variable name, or -f is supplied with a name that is not a function.

You can not use export $VARIABLE, because the shell would expand $VARIABLE to its content before calling export.