Fix a few grammar problems in the documentation and comments
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
index 1ee5110..5373acd 100644
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -104,7 +104,7 @@
:mod:`ast` Helpers
------------------
-Apart from the node classes, :mod:`ast` module defines these utility functions
+Apart from the node classes, the :mod:`ast` module defines these utility functions
and classes for traversing abstract syntax trees:
.. function:: parse(source, filename='<unknown>', mode='exec')