Why we didn't use DID instead?

[Niveen (Palestine)]

English Grammar Tests, Elementary Level

ESL/EFL Test #95 "auxiliary verbs: was, did, have", question 10

How many times ......... your travel documents checked before you boarded the airplane?

(a) was
(b) were
(c) did
(d) had

English Grammar Tests, Elementary Level

ESL/EFL Test #95 "auxiliary verbs: was, did, have", answer 10

How many times were your travel documents checked before you boarded the airplane?

Correct answer: (b) were

Your answer was: incorrect
How many times did your travel documents checked before you boarded the airplane?
_________________________

Hello,

why we didn't use did instead??

All the best

Niveen (Palestine)

[Conchita]

How many times were your travel documents checked... ?

This sentence is in the passive voice, because the fact that the documents were checked is more important than who checked them.

To make this sentence active, we need a subject:

How many times did the airport authorities (or: they) check your travel documents...?