A school may, at its discretion, rescind an offer of acceptance for inadequate academic performance (among other things). What that means is open to interpretation by the school. If you are planning on getting a couple As/Bs and a C, you should be fine. All C's might be different. I think it depends too much on the individual school to really say with any certainty. There was another thread about this yesterday that might be worth looking up, as some of the more experienced SDN users weighed in on the issue.