Unqualified Element without using xs:any

Would someone please explain the approach used to create a schema capable of 
validating the following xml document without using "xs:any".
In particular, I'm having difficulty getting past the default Namespace of 
the "C" and "D" elements contained within the "B" element.  I have tried 
several different options and the only one that has worked is when element 
"B" is defined as <xs:any namespace="##any"/>. What other options are there?

Thanks
Don

<aaa:A xmlns:aaa="urn:a" version="1.0">
	<aaa:A1>
		<bbb:B xmlns:bbb="urn:b">
			<C>
				<D>Text</D>
			</C>
			<C>
				<D>Text</D>
			</C>
		</bbb:B>
	</aaa:A1>
</aaa:A>