Sitemaps - do I need to submit each sitemap in sitemap_index.xml to Google Webmaster tools?

Question

I am having a Wordpress blog on my CentOS server. There is no sitemap.xml in the root directory but there is sitemap_index.xml file in the root directory which contains the following code:

<?xml-stylesheet type="text/xsl" href="http://mywebsite.com/wp-content/plugins/wordpress-seo/css/xml-sitemap-xsl.php"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
    <sitemap>
        <loc>
            http://mywebsite.com/post-sitemap.xml
        </loc>
        <lastmod>
            2012-12-18T19:47:47+00:00
        </lastmod>
    </sitemap>

    <sitemap>
        <loc>
            http://mywebsite.com/page-sitemap.xml
        </loc>
        <lastmod>
            2012-12-18T17:32:49+00:00
        </lastmod>
    </sitemap>
</sitemapindex>

My question: Which sitemap should I submit to Google Webmasters Tools? Options are:

1. Only sitemap_index.xml
2. Only post-sitemap.xml and page-sitemap.xml
3. All 3 (sitemap_index.xml, post-sitemap.xml and page-sitemap.xml)
4. Any other, please let me know.

Answer 1

Just submit the master sitemap. It's purpose is to tell them about the other sitemaps so there is no need to submit them.

Answer 2

According to Google Webmaster Tools support article http://support.google.com/webmasters/bin/answer.py?hl=en&answer=71453

When you've created your Sitemap index file, save it and submit it to Google. As long as you've uploaded and saved all your Sitemaps, you don't need to submit each Sitemap individually. Just submit the Sitemap index file and you're good to go. You can submit up to 500 Sitemap index files for each site in your account.

Sample code on their page