The conference hall.............................before they arrived.

[abo.omar]

The conference hall.............................before they arrived.
a-was cleaned
b-had been cleaned
c-has been cleaned
d-cleaned
My answer is had been cleaned because of the word key before.
Can we use was cleaned as the context is not so enough?
The source is an Egyptian secondary test.

 

[Rover_KE]

Yes, but I'm not sure what you mean by 'as the context is not so enough'.

 

[jutfrank]

abo.omar means there's not enough context to make the past perfect the best answer. Which is absolutely right.

 

[emsr2d2]

abo.omar means there's not enough context to make the past perfect the best answer. Which is absolutely right.

No doubt, but there's still the issue that "the context is not so enough" is not grammatical, particularly the last two words together.