Fix lab 1 issues

Introduction to D/lecture/arrays/array_setting.d

@@ -5,7 +5,7 @@ void main()
     int[] b = [1, 2, 3, 4, 5];
     a = 3;                     // set all elements of a to 3
     a[] = 2;                   // same as `a = 3`; using an empty slice is the same as slicing the full array
-    b = a[0 .. $];             // $ evaluates to the length of the array (in this case 10)
+    b = a[0 .. $];             // $ evaluates to the length of the array (in this case 3)
     b = a[];                   // semantically equivalent to the one above
     b = a[0 .. a.length];      // semantically equivalent to the one above
     b[] = a[];                 // semantically equivalent to the one above

Introduction to D/lecture/arrays/vector.d

@@ -4,6 +4,8 @@ void main()
     int[] b;
     int[] c;
 
+    b.length = 3;
+    c.length = 3;
     b[] = a[] + 4;         // b = [5, 6, 7]
     c[] = (a[] + 1) * b[];  // c = [10, 18, 28]
 }

docs/intro/quiz/slice.md

@@ -6,7 +6,7 @@ nav_exclude: true
 ## Slices quiz
 
   {% assign q1_text = "Why, for the previous example, the lengths of a and b are different?" %}
-  {% assign q1_choices = "`a` and `b` have the same lengths| `b` refers the same data as `a`, but it has no length constraints| a copy of `a` was saved into `b`, a dynamic array, and then the value 5 was appended to the dynamic array| operator `~` works for slices, but it has no impact on static arrays" | split: "| " %}
-  {% assign q1_feedbacks = "`a` is a static array, so it's length is fixed, but we can still append data in that particular memory zone through a different reference| Correct!| `a` is a static array, so it's length is fixed, but we can still append data in that particular memory zone through a different reference| `a` is a static array, so it's length is fixed, but we can still append data in that particular memory zone through a different reference" | split: "| " %}
-  {% assign q1_correct = 1 %}
+  {% assign q1_choices = "`a` and `b` have the same lengths | `b` refers the same data as `a`, but it has no length constraints so `5` is simply appended in place | `b` is allocated a new memory region when `5` is concatenated to it | operator `~` works for slices, but it has no impact on static arrays" | split: "| " %}
+  {% assign q1_feedbacks = "`a` is a static array, so it's length is fixed, but appending data to it through `b` results in: allocating new memory for `b`, copying the contents of `a` to `b` and adding the new elements (`5` in this case) to the end of the array| `a` is a static array, so it's length is fixed, but appending data to it through `b` results in: allocating new memory for `b`, copying the contents of `a` to `b` and adding the new elements (`5` in this case) to the end of the array| Correct!| `a` is a static array, so it's length is fixed, but appending data to it through `b` results in: allocating new memory for `b`, copying the contents of `a` to `b` and adding new elements (`5` in this case) to the end of the array | split: "| " %}
+  {% assign q1_correct = 2 %}
   {% include mc-quiz.html text=q1_text choices=q1_choices answer=q1_correct feedback=q1_feedbacks %}