How to do an OR within SELECT for a variable

My XML can look like this :

<A>
   <B>
      <C>
         <D ID="1">data</D>
      </C>
   </B>
</A>

or 

<A>
   <B>
      <X>
         <D ID="2">data</D>
      </X>
   </B>
</A>

I set a variable like this :

<xsl:variable name="var" select="A/B/C/D/@ID" />

or

<xsl:variable name="var" select="A/B/X/D/@ID" />

Can I use something like :

<xsl:variable name="var" select="A/B/C|X/D/@ID" />

I think this gets interpretted as 'A/B/C' or 'X/D/@ID'

Thanks in advance,

Steve