Supply missing word in new datetime docs, aggravated by copy-paste-edit.

Doc/api/concrete.tex

@@ -2756,7 +2756,7 @@ Macros to create objects:
   \versionadded{2.4}
 \end{cfuncdesc}
 
-Macros to extract fields from date objects.  The argument must an
+Macros to extract fields from date objects.  The argument must be an
 instance of \cdata{PyDateTime_Date}, including subclasses (such as
 \cdata{PyDateTime_DateTime}).  The argument must not be \NULL{}, and
 the type is not checked:
@@ -2776,7 +2776,7 @@ the type is not checked:
   \versionadded{2.4}
 \end{cfuncdesc}
 
-Macros to extract fields from datetime objects.  The argument must an
+Macros to extract fields from datetime objects.  The argument must be an
 instance of \cdata{PyDateTime_DateTime}, including subclasses.
 The argument must not be \NULL{}, and the type is not checked:
 
@@ -2800,7 +2800,7 @@ The argument must not be \NULL{}, and the type is not checked:
   \versionadded{2.4}
 \end{cfuncdesc}
 
-Macros to extract fields from time objects.  The argument must an
+Macros to extract fields from time objects.  The argument must be an
 instance of \cdata{PyDateTime_Time}, including subclasses.
 The argument must not be \NULL{}, and the type is not checked: