Need help with an XPath expression in XSLT

I have a document with the following structure:

<root>
  <A>
    <B>1</B>
    <C>
      <D>abc</D>
    </C>
  </A>
  <A>
    <B>2</B>
    <C>
      <D>xyz</D>
    </C>
  </A>
</root>

I have an XSLT transformation where I need to add an attribute to any given
element <D> if the value of <B> is 1 where <D> and <B> have the same
ancestor <A>.

I'm having trouble getting the right expression on my <xsl:if> element to
test the value of the right <B> element given a context node of <D>.

Brenda Bell
Sr. Software Architect
Juice Software, Inc.
Phone: 603.428.3994
Cell: 603.494.8206
Fax: 603.428.8713
Email: bbell@juicesoftware.com