XML Schema

Hi All,
In my complex type I had a choice. If I use choice it accepts only C or D...but why my problem is it should be AT LEAST ONE C / D.

It can be C, D, C and D (At Least One)...can any one help me out how to do.

It should be C or D or C & D.....


<xsd:complexType name="Head">
<xsd:sequence>
<xsd:element name="A" type="xsd:string" minOccurs="1" maxOccurs="1"/>
<xsd:element name="B" type="xsd:string" minOccurs="1" maxOccurs="1"/>

<xsd:choice>
<xsd:element name="C" type="xsd:string" minOccurs="0" maxOccurs="1"/>
<xsd:element name="D" type="xsd:date" minOccurs="0" maxOccurs="1"/>
</xsd:choice>


</xsd:sequence>
</xsd:complexType>


Thanks,

KVRAO