fix three trivial typos.

pep-0252.txt

@@ -158,7 +158,7 @@ Specification of the class-based introspection API
 
     In the discussion below, I distinguish two kinds of objects:
     regular objects (like lists, ints, functions) and meta-objects.
-    Types and classes and meta-objects.  Meta-objects are also regular
+    Types and classes are meta-objects.  Meta-objects are also regular
     objects, but we're mostly interested in them because they are
     referenced by the __class__ attribute of regular objects (or by
     the __bases__ attribute of other meta-objects).
@@ -225,7 +225,7 @@ Specification of the class-based introspection API
        meta-objects, the bases.  An absent __bases__ is equivalent to
        an empty sequence of bases.  There must never be a cycle in the
        relationship between meta-objects defined by __bases__
-       attributes; in other words, the __bases__ attributes define an
+       attributes; in other words, the __bases__ attributes define a
        directed acyclic graph, with arcs pointing from derived
        meta-objects to their base meta-objects.  (It is not
        necessarily a tree, since multiple classes can have the same
@@ -555,7 +555,7 @@ C API
     - But now for a more complicated case.  The approach described
       above is suitable for most built-in objects such as lists,
       strings, numbers.  However, some object types have a dictionary
-      in each instance that can store arbitrary attribute.  In fact,
+      in each instance that can store arbitrary attributes.  In fact,
       when you use a class statement to subtype an existing built-in
       type, you automatically get such a dictionary (unless you
       explicitly turn it off, using another advanced feature,