my @list1 = $doc->selectNodes("A/B");
my @list2 = $doc->selectNodes("A/C/D");
while (@list1 or @list2) {
    my ($B,$D) = ('-EMPTY-','-EMPTY-');
    if (@list1) {
        my $t = shift @list1;
        $B = $t->nodeValue();
    }
    if (@list2) {
        my $t = shift @list1;
        $D = $t->nodeValue();
    }
    print "$B / $D \n";
}