Grammer question

There was no food left when I returned. They ___ everything!

The answer is (had eaten)
Why did we use had eaten not (ate)

'had eaten' is past tense

is it the same / ? can I use any one of them?

HAD EATEN is in the present perfect tense. We are thinking more about the result and NOT the time it took place. The present perfect tense is formed using 'has' or 'have' and the past participle of the main verb. When an action has JUST taken place and you are thinking more of the result and not the time, it should be in the present perfect form. There are 3 major types of tenses in English but there are 9 tenses. These tenses are very confusing if not understood. You can funmail me for more details about Grammar.

Luret

Because 'ate' is present tense (ie. they ate the apples happily).

Had eaten is past tense, it happened in the past.

Sorry I made a mistake. Had eaten is in the past perfect tense.