I incorrectly said increases from 8 hrs to 10rs, but I meant  

(b) limits you to 8 hrs of flight time in 24 consecutive hours.

Assume you got 8 hrs of flight time ending right at your 14th hour of duty.   You look back 24 hours and see you are within limits.   You go on rest and go home for 10 hours.   When you come back in the morning, can you fly?   Well, if you looked back 24 consecutive hours, you already have 8 hours of flight time on you still.  You cannot fly.

So, they created an exception for those maintaining a regurlarly scheduled duty period.   GOM pilots, for instance, operating under (c), can come back on duty and ignore the 8 hour flight time limit in 24 consecutive hours and fly, provided they were scheduled for no more than  8 hours of flight time for this 14 hour duty period.

(c) is all about flight time, not duty time.   It gives an operator the chance to exceed the 8 hour flight time in 24 consecutive hours limit.