C-Class IP address means that it belongs to a range that starts at 192.0.0.1 and ends at 126.96.36.199. The class of IP address describes in what range the first block of the IP address will be from. A block has IP ranges that first block starts from 0. to 127., B from 128. to 191., C from 192. to 223, D from 224. to 239. and E from 240 to 255.
So for example, these random IPs, would belong to such categories:
B - 194.XXX.222.12
A - 91.24.x.44
C - 222.111.x.33
D - 188.8.131.52
E - 255.255.255.0
You can definately have 2 IP addresses assigned for your website. The visitors then would have 50/50 chance of visiting through one or another IP address, so if visitor would fail through one of the IP addresses, by refreshing the address there would be a change that the connection would be done through another IP address. But if you wish to have as a backup option that is active only when main IP is inactive it is not possible as I know, since A records does not have an option that would allow to set a priority on the records.
If you will choose to set your domain with 2 IP addresses, make sure you check with your website programmers, since you might need of linking the websites/databases if the IP addresses will be of 2 separate servers.