grammar - Possible positions for the word currently

I was discussing the question of correct word placement in english with a coworker but since we both aren't native speakers we did not come to a conclusion.

Here is an example: Given the sentence

We have no open positions available.

which of the following placements of the word currently are valid?

Is there a simple rule which explains this?

1. Currently we have no open positions available.


2. We currently have no open positions available.


3. We have currently no open positions available.


4. We have no open positions currently available.


5. We have no open positions available, currently.

Answer

They are all correct, though I'd add a few commas here and there. The rule that dictates where adverbs should go is subtle. Adverbs go just before the word or phrase that the adverb is modifying. Essentially 1 - 3 and 5 mean the same thing. Number 5 is least natural because the modifier is at the end, but you've made it into an adverbial phrase.

At this time, we have no open positions available.

Really, there are no job openings. End of story.

Number 4 is a little different. 'Currently' is specifically modifying 'available'.

We have no open positions, that are at this time, available.

There might be job openings, but for whatever reason, they aren't being filled right now.