typo

Exercises/ex6_2.md

@@ -9,7 +9,7 @@
 
 *Files modified:* `structure.py`, `stock.py`
 
-In the last exercise, you create a class `Structure` that made it easy to define
+In the last exercise, you created a class `Structure` that made it easy to define
 data structures.  For example:
 
 ```python