Normally an interrogative phrase of this type starts
with a verb. In other words, we find here the same inversion
of subject and verb that we have already seen in many
other circumstances, like conjunctions,
clauses and word
order in a phrase.
In some cases it is possible to form an interrogative
phrase without the inversion of subject and verb. But
then the pronunciation of the question must be stronger
than usually. Else the one listening cannot understand
that it is a question.