html
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<select id="num">
<option value="0">请选择</option>
<option value="1">111</option>
<option value="2">222</option>
<option value="3">333</option>
<option value="4">444</option>
</select>
jQuery
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方法1：
var val = $('#num').val();
方法2：
var val = $('#num option:selected').val();