C#中如何遍历xml并取对应节点的值
<system>
<caption>开票子系统</caption>
<nodes step="1" flag="0">
<control>
<action>keyboard</action>
<key>ENTER</key>
</control>
</nodes>
</system>
<system>
<caption>等候提示</caption>
</system>
<system>
<caption>操作员登录</caption>
<nodes step="2" flag="0">
<data>
<value>string</value>
</data>
</nodes>
<nodes step="3" flag="0">
<control>
<action>keyboard</action>
<key>ENTER</key>
</control>
</nodes>
</system>
<system>
<caption>系统</caption>
<nodes step="4" flag="0">
<control>
<action>keyboard</action>
<key>ALT_LOCK>fy<ALT_UNLOCK</key>
</control>
</nodes>
<nodes step="5" flag="0">
<control>
<action>keyboard</action>
<key>ALT_LOCK>c<ALT_UNLOCK</key>
</control>
</nodes>
<nodes step="6" flag="0">
<control>
<action>keyboard</action>
<key>LEFT</key>
</control>
</nodes>
<nodes step="7" flag="0">
<control>
<action>keyboard</action>
<key>DOWN</key>
</control>
</nodes>
<nodes step="8" flag="0">
<control>
<action>keyboard</action>
<key>ENTER</key>
</control>
</nodes>
</system>
怎样区分每个System节点和nodes节点呢?