word order inversion after 'no circumstances' (must you)

[Emad]

I do not know the answer for this question :

Under no circumstances ..........press that button .

a)you must b)must you c) you should d)you will

choose the correct answer ,and i will be thoughtful to reason your choose.

Regards
Emad

[Alan]

Hi Emad,

When you begin a sentence with words such as not only/never/hardly and this one Under no circumstances we usually invert the order and write verb+subject. So we would write: Under no circumstances must you ...

Alan
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[Emad]

Thanks Alan for explaining .

Regards
Emad