The correct answer is b.
Hardly, as an adverb means "just", hardly, in this context is acting as a limiting modifier of the word ever. <em>Hardly ever</em> means very occasionally. We may use words like it to emphasize how infrequently an action takes place. You should note also that there could be other ways to give quite the same meaning, like when you use <em>rarely</em> or <em>seldom</em>, but, hardly ever has also a <u>negative</u> connotation.
Answer:
Far
Explanation:
The text seems to indicate that all around the wreck is sand as far as the eye can see, hence boundless.
The prehistoric monument caught everyone's eyes, a piece of the past to not be forgotten.
