Can nucleotides A and A establish a bond? or U&U, C&C, G&G?

No.

The statement clears:

there could be hydrogen bonds established between any pair of (A,U), (U,A), (G,C) or (C,G) nucleotides, but not for the other cases.

Yep, I was getting wrong answer and didn't know what's the problem! Now, it's clear. Thanks anyway.