(you could use the term multiverse if you prefer) then the conclusion that the Universe had a cause implies the cause was supernatural. In other words the creation of the Universe was via spiritual or god-like mechanisms.

Alternatively, take the infinitely rebounding universe - going from crunch to bang to crunch, etc, where the crunch hides all record of the past cycles through the conversion of matter to energy (thus, the term: "the unknowable past"). This idea contradicts premise B above. But that does't help: it raises a more worrisome (to me) idea that something exists forever with no cause. 

These metaphysical dead ends are certainly what have helped spawn the major religions and are of no end of frustration to us atheists.