In order to invert, the subject verb object order of a normal sentence is changed in some way. 300 men would stand in the pass. In the pass would stand 300 men. (adverb of place + complete verb ...

If we are told that we 'must' do something, like complete homework, the modal verb 'must' indicates a high level of modality. There is no argument. The homework has to be done. But if we are told ...