Position of Adverbs

Hi,

I have a problem with the key of the following quiz.

Our meetings are ......held in the top floor conference room.
(A) monthly
(B) every week
(C) always
(D) once

I think (C) always is correct, because it's the only indefinite frequency adverb and should be located in the mid position. But the key is (B) every week.
Am I missing something?

Thanks for any help.