Note that to add thumbnail URL on WordPress so that videos on pages can be indexed and served on as video " Embed video with a featured image" (Option C)
To add a thumbnail URL for videos on WordPress, you can embed the video in your pages or posts and set a featured image. This featured image will serve as the thumbnail.
Simply use the video embed option in the WordPress editor, and then set a featured image for the post or page to ensure proper indexing and display of the video with its thumbnail.
Thus, the right answer is Option C.
Full Question:
Although part of your question is missing, you might be referring to this full question:
How to add thumbnail URL on WordPress so that videos on pages can be indexed and served on as video?
a) Utilize custom CSS for thumbnail integration
b) Install a video indexing plugin
c) Embed video with a featured image
d) Adjust permalink settings for video visibility