We recommend that you use a canonical URL from the duplicated version back to the original source if you're testing 2 (or more) variations of a page all with similar content.

For example;

You would leave Page A as normal and using your SEO plugin of choice, set the canonical URL of Page B, C & D with the URL of Page A.

If you are looking for an in-depth, more extensive explanation of canonical URLs, please check out this article.

Here are a few guides for the most common SEO Plugins in WordPress;