Google determines what to display as the text may be more relevant to the search query compared to your meta description tag.

I agree that Thomasnet is a waste of money... I haven't seen any increases in organic positions with clients that paid to have the Thomasnet listing

Using option B allows you to gather info on them before the receive access to ebook. However, if you were to block access to the page, option c would work to still gather user info. You can also track the pdf's off the landing page but this allows the user to have a local copy and 'share' your content without registering their information.

I would personally recommend option C as long as it's a hidden or protected page.