Which sentence below shows correct use of an em dash?
we’re hosting a party – you are invited, of course – later this month.
we’re hosting a party you are invited – of course later this month.
we’re – hosting a party, you are invited of course later – this month.
we’re hosting – a party – you are invited of course, later, this month.

A. We're hosting a party -- you are invited, of course -- later this month. 

The trick to figuring out them em dash is that if you remove the part inside ('you are invited, of course'), the rest of the sentence still needs to make sense with that bit removed ('we're hosting a party later this month'). 

Option A

Explanation:

The answer is "We’re hosting a party – you are invited, of course – later this month." or option A. A em dash is a dash that is set in sentences to show a difference or change in tone. First remove the dashes from the sentence of option A. "We’re hosting a party you are invited, of course later this month." In the sentence you will see that there's a shift in tone in three different areas here you can see that there is a tone when they say "we're hosting a party" so set a dash there, another shift in tone when they say "you are invited", then there's a shift in tone when they say "later this month."

Hope this helps.

1. All we Karamazovs are such insects,  and. . .that insect lives in you, too.  

metaphor  

2. Why then, O brawling love, O loving hate,  O anything, from nothing first create,  O heavy lightness! Serious vanity!    

oxymoron  

3. I was quaking from head to foot,  and could have hung my hat on my  eyes, they stuck out so far.  

hyperbole  

Explanation:  

1. metaphor is an implied comparison; it is when you are saying that something is something else.  

"we Karamazovs are such insects". The speaker compares his family to insects by saying that they are insects.    

2. oxymoron is a combination of two words that seem to be contradictory.  

"loving hate" is an example of such a combination, and so is "heavy lightness."  "Serious vanity" and "brawling love" were also written with an oxymoron in mind.

3. hyperbole is exaggeration used for dramatic effect.  

"I was quaking from head to foot,  and could have hung my hat on my  eyes, they stuck out so far." The whole excerpt is an excellent example of a hyperbole because it is an obvious exaggeration.