diff --git a/mod/quiz/lang/en/quiz.php b/mod/quiz/lang/en/quiz.php
index d71908c87567a..a0989b78ddff7 100644
--- a/mod/quiz/lang/en/quiz.php
+++ b/mod/quiz/lang/en/quiz.php
@@ -159,6 +159,7 @@
 $string['categorynoedit'] = 'You do not have editing privileges in the category \'{$a}\'.';
 $string['categoryupdated'] = 'The category was successfully updated';
 $string['close'] = 'Close window';
+$string['closed'] = 'Closed';
 $string['closebeforeopen'] = 'Could not update the quiz. You have specified a close date before the open date.';
 $string['closepreview'] = 'Close preview';
 $string['closereview'] = 'Close review';
diff --git a/question/type/multichoice/questiontype.php b/question/type/multichoice/questiontype.php
index aa555188c98e2..d82366f7cf357 100644
--- a/question/type/multichoice/questiontype.php
+++ b/question/type/multichoice/questiontype.php
@@ -358,6 +358,23 @@ function print_question_formulation_and_controls(&$question, &$state, $cmoptions
         include("$CFG->dirroot/question/type/multichoice/display.html");
     }
 
+    function compare_responses($question, $state, $teststate) {
+        if ($question->options->single) {
+            if (!empty($state->responses[''])) {
+                return $state->responses[''] == $teststate->responses[''];
+            } else {
+                return empty($teststate->response['']);
+            }
+        } else {
+            foreach ($question->options->answers as $ansid => $notused) {
+                if (empty($state->responses[$ansid]) != empty($teststate->responses[$ansid])) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+
     function grade_responses(&$question, &$state, $cmoptions) {
         $state->raw_grade = 0;
         if($question->options->single) {