SHOULD HAVE OR SHOULD'VE, NOT SHOULD OF

I should have been paying attention in English class.
I should've been paying attention in English class.
I should of been paying attention in English class.

COULD HAVE OR COULD'VE, NOT COULD OF

I could have done better at English.
I could've done better at English.
I could of done better at English.

WOULD HAVE OR WOULD'VE, NOT WOULD OF

I would have done better if I'd only listened.
I would've done better if I'd only listened.
I would of done better if I'd only listened.

MUST HAVE OR MUST'VE, NOT MUST OF

I must have been ridiculed for using such poor grammar.
I must've been ridiculed for using such poor grammar.
I must of been ridiculed for using such poor grammar.