while (<>) {
    chomp;
    my @fields = split /\t/;
    for ( splice(@fields, 3) ) {
        print(join("\t", @fields, $_), "\n");
    }
}

##</code><code>##

while (<>) {
    (my $common, $_) = /^((?:[^\t]*\t){3})(.*)/;
    for ( split /\t/ ) {
        print("$common\t$_\n");
    }
}