Xpath>如何根据属性和内容选择节点？

Sample XML:

示例XML：

<assignments>
<assignment id="911990211" section-id="1942268885" item-count="21" sources="foo">
    <options>
        <value name="NumRetakes">4</value>
        <value name="MultipleResultGrading">6</value>
        <value name="MaxFeedbackAttempts">-1</value>
        <value name="ItemTakesBeforeHint">1</value>
        <value name="TimeAllowed">0</value>
    </options>
</assignment>
<assignment id="1425185257" section-id="1505958877" item-count="4" sources="bar">
    <options>
        <value name="NumRetakes">0</value>
        <value name="MultipleResultGrading">6</value>
        <value name="MaxFeedbackAttempts">3</value>
        <value name="ItemTakesBeforeHint">1</value>
        <value name="TimeAllowed">0</value>
    </options>
</assignment>
<assignments>
<assignments>
<assignmen