How To Join Multiple XPath Criteria

I have loaded an HTML table into an XmlDocument object.  I am calling SelectNodes with the XPath query shown below.  It fails with the error message "Expression must evaluate to a node-set."  If I call either one of the conditions alone it works.  What is the correct syntax to join these two condtions into one query?

string sXpathQuery = "/table/tr/td[19][text()='M'] and /table/tr/td[20][text()='0']";

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