The correct answer is 'going on slowly'. 'Hang fire' is an idiomatic phrase which means to wait to take action or to await further action. Example: The project had hung fire for several years because of lack of funds.

What does the expression hanging fire mean?

The phrase "to hang fire" has come to mean a delay in progressing, for example from one task to another.

Where did hang fire come from?

It dates from a time when firearms were loaded using a gunpowder charge poured from a flask, which was then ignited by a spark from a flint striking against an iron plate.