It is not. If you want to use b), you have to:
- state it explicitely ;
- keep a copy of the sources of every version you distribute in binary form for 3 years in case it is no longer available at its original location.
I don't think it is a good thing, but that's what the GPL says. That's one of the reasons why I avoid its use when I can...
You're right. I just finished reading the discussion on the bug tracker about GPL compliance which made me realize the obligations that that clause imposes.
*heads off to review alternative software licenses*