Which sentence uses the word eat in the past perfect tense?

a. Sheila ate her lunch in the cafeteria. * (my answer, is it correct?)
b. They eat lunch together everyday
c. Douglas has eaten all the potato chips
d. The twins had eaten pizza before they arrived

No.

Scroll down and find the chart that demonstrates the different perfect tenses:
https://learningenglish.voanews.com/a/everyday-grammar-have-you-perfected-the-perfect-tenses/3137265.html

Let us know what you decide.

Yes, you are correct! Sentence d. "The twins had eaten pizza before they arrived" uses the word eat in the past perfect tense.

To determine the tense of a verb, you need to identify the helping verb (also called auxiliary verb) and the main verb. In this case, the helping verb is "had" and the main verb is "eaten." The helping verb "had" indicates that the action of eating occurred before another past action, which is indicated by the word "arrived." Therefore, this sentence is in the past perfect tense.