+---+
| A | -+
+---+  |
  |    |
  |    |
  |    |
+---+  |
| B |  |
+---+  |
  |    |
  |    |
  |    |
+---+  |
| C |  |
+---+  |
  |    |
  |    |
  |    |
+---+  |
| D | -+
+---+