How to populate form dropdown by using a link

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Hey Guys,
So I've been trying my best to figure this out on my own, but I'm completely stuck. I have a form for users to fill out. I also have links spread throughout my site that takes them to this form. I want to populate one of the dropdowns in that form based on where they came from. My dropdown is called id="show_customer3".

    <div id="show_demo2" >
      <p>Where did you hear about us?:</p>
    </div>
<!--This is where the user selects which product they own.-->
  <td colspan="1" rowspan="1">
    <div id="show_customer3" style="display: none;">
      <p><select id="WHAT" name="WHAT" size="1">
        <option selected="selected" value="">Select One</option>
        <option value="Item 1">Item 1</option>
        <option value="Item 2">Item 2</option>
        <option value="Item 3">Item 3</option>
        <option value="Item 4">Item 4</option>
        <option value="Item 5">Item 5</option>
        <option value="Item 6">Item 6</option>
        <option value="Item 7">Item 8</option>
        <option value="Item 9">Item 9</option>
        <option value="Item 10">Item 10</option>
        <option value="Item 11">Item 11</option>
        <option value="Item 12">Item 12</option>
      </select></p>
    </div>

    <div id="show_demo3" style="display: none;">
      <p>
        <input maxlength="64" name="WHERE" size="30" type="text" value="" />
      </p>
    </div>
  </td>

I was thinking my link would look something like:

mysite.com/thispage#show_customer3;selected="Item 1"

I appreciate any help. Thanks!