Phrasal verbs: 'went out' vs. 'go out'

[DESIRE]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #120 "Perfect Tenses", question 9

They were eating dinner when the lights ......... out.

(a) go
(b) are going
(c) went
(d) goes

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #120 "Perfect Tenses", answer 9

They were eating dinner when the lights went out.

Correct answer: (c) went

Your answer was: incorrect
They were eating dinner when the lights go out.
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why are we using here went out.
the only reason coming through my mind is the tense harmony.
am ı right?
ı couldn't understand.please answer me.

with my regards

DESİRE

[Mister Micawber]

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Yes, you are right. When indicates that the two events happened at the same time, and were eating is a past verb form; therefore, the other verb should be in a past verb form.
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Native English teacher at Mister Micawber's