Data Structure Revisions

Added in mention of format method in More About Strings.
Typo.

data_structures.md

@@ -215,9 +215,9 @@ Remember that if you want to make a copy of a list or such kinds of sequences or
 
 ## More About Strings {#more-strings}
 
-We have already discussed strings in detail earlier. What more can there be to know?  Well, did you know that strings are also objects and have methods which do everything from checking part of a string to stripping spaces!
+We have already discussed strings in detail earlier. What more can there be to know?  Well, did you know that strings are also objects and have methods which do everything from checking part of a string to stripping spaces?  In fact, you've already been using a string method... the `format` method!
 
-The strings that you use in program are all objects of the class `str`.  Some useful methods of this class are demonstrated in the next example. For a complete list of such methods, see `help(str)`.
+The strings that you use in programs are all objects of the class `str`.  Some useful methods of this class are demonstrated in the next example. For a complete list of such methods, see `help(str)`.
 
 Example (save as `ds_str_methods.py`):