Small improvement to help files

lang/en_utf8/help/quiz/random.html

@@ -7,13 +7,17 @@
 
 <p>This means that different students are likely to get a different selection 
    of questions when they attempt this quiz.  When a quiz allows multiple 
-   attempts for each student then each attempt will also contain a new 
+   attempts for each student then each attempt is likely to contain a new 
    selection of questions.</p>
    
-<p>The same question will never appear twice in a quiz.  If you include several 
+<p>The same question will never appear twice in an attempt.  If you include several 
    Random Questions then different questions will always be chosen for each of them. 
    If you mix Random Questions with non-random questions then the random questions 
-   will be chosen so that they do not duplicate one of the non-random questions.</p>
+   will be chosen so that they do not duplicate one of the non-random questions.
+   This does imply that you need to provide enough questions in the
+   category from which the random questions are chosen, otherwise the student will
+   be shown a friendly error message. The more questions you provide the more
+   likely it will be that students get different questions on each attempt.</p>
 
 <p>The grade for the randomly chosen question will be rescaled so that the 
    maximum grade is what you have chosen as the grade for the Random Question.</p>

lang/en_utf8/help/quiz/randomsamatch.html

@@ -11,4 +11,9 @@
 
 <p>The questions and answers are randomly drawn from the pool of
    "Short Answer" questions in the current category.  Each attempt
-   on a quiz will have different questions and answers.</p>
+   on a quiz may therefore have different questions and answers.
+   You must make sure that the category contains enough unused
+   short-answer questions, otherwise the student will be shown
+   a friendly error message. The more short-answer questions you
+   provide the more likely it is that students will see a new
+   selection on each attempt.</p>