Which sentence uses apostrophes correctly?

a
You're certainly mistaken that your efforts will go unheralded; it's very certain that the conference will go well, since its viewership will be immense.
b
You're certainly mistaken that your efforts will go unheralded; its very certain that the conference will go well, since its viewership will be immense.
c
Your certainly mistaken that you're efforts will go unheralded; it's very certain that the conference will go well, since its viewership will be immense.
d
You're certainly mistaken that your efforts will go unheralded; it's very certain that the conference will go well, since its viewership will be immense.