A set of buttons that are styled like standard Salesforce buttons. This component must be a child
component of an <apex:pageBlock>.
Note that it is not necessary for the buttons themselves to be direct children of the
<apex:pageBlockButtons> component—buttons that are located at any level within an
<apex:pageBlockButtons> component are styled appropriately.

A.
apex:includeScript

B.
apex:commandButton

C.
apex:pageBlockButtons

D.
apex:form