Does the following Diffie-Hellman problem hold in bilinear groups $G\times G \rightarrow G_T$
Hint: suppose we modify the problem so that $r, a, b, z$ are selected uniformly randomly from the interval $[1, p-1]$; how do the probability distributions of $(g^{ra}, g^{rb}, g^{rab})$ and $(g^{ra}, g^{rb}, g^{rz})$ compare?

Hint: if we actually select $r, a, b, z$ from $\mathbb{Z}_p$, what is the probability that at least one of them are selected outside the interval $[1, p-1]$?  Can you show that this probability is negligible?