Which element is present in both the Latin terms for "day" (diēs) and the phrase meaning "they will have found"?

The correct choice is based on the analysis of the Latin terms involved. The Latin word for "day" is "diēs," and it contains the vowel "E." This vowel is a significant component of the word itself.

In the phrase meaning "they will have found," which is "invenient" (the future perfect tense of the verb "invenio"), the same vowel "E" also appears in the word "invenient." This shows that "E" is indeed present in both the term for "day" and the phrase that describes the action of finding.

The presence of "E" in both "diēs" and "invenient" makes it the correct answer, demonstrating a consistent linguistic element that links both terms. Other choices do not share this commonality across the two terms provided.