How to parse "$70,000/yr for 9 months' employment payable over 12 months"?
Option B.

Typically this confusing language reflects that you only have to teach for 9 months, and your salary is tied to your teaching responsibilities. So the university gives you $7777/month for 9 months and $0 for the other three. You can then supplement your income for the remaining three months. In particular, many research grants allow you to cover part or all of your own summer salary at your usual rate -- so if you win such a grant, you can actually gross $7777 every month and end up making a total of $93K per year.

In your case (perhaps because it's a teaching college and research grants are unusual?), they will "pay the salary over 12 months," which works out to $5833/month. This will save you the trouble of having to set money aside during the year and use it during the summer. 

Note, your college may still require you to be "productive" over the summer (for certain values of "productive"). For that matter, they may provide the opportunity to take on additional paid work (i.e., teaching summer classes).