Which sentence does not contain misplaced or dangling modifiers?

a.
the directions spoken too quietly to the store were misunderstood.

b.
the directions to the store were misunderstood, spoken too quietly.

c.
spoken too quietly, the directions to the store were misunderstood.

d.
spoken too quietly to the store, the directions were misunderstood.

Alright, let us give this one a shot as well.

A. The directions spoken too quietly to the store were misunderstood.

Were the directions being given to the store? I think probably not, as a store would most likely always misunderstand your directions.

B. The directions to the store were misunderstood, spoken too quietly.

This sentence properly conveys the message, but it's a little awkward, and the last phrase seems tacked-on at the end there. Next!

C. Spoken too quietly, the directions to the store were misunderstood.

Here, we have a complete thought. Someone spoke the directions to the store too quietly, and the receiver of those directions misunderstood them.
This looks like a good choice, but let us examine the last choice for the heck of it.

D. Spoken too quietly to the store, the directions were misunderstood.

Yet again, someone is giving the store directions again. Silly people, don't they know that stores always misunderstand?

Your correct answer would be choice C.
Hope that helped! =)