Trivial / Non trivial all pass system

у меня такая задача, помогите пожалуйста ее решить. https://imgur.com/a/3nVTe8t

Explain if a cascade of two of the above systems (AB, AC, or BC) leads to a non-trivial all-pass system. If yes, what is the order of that all-pass system ? Note: a trivial all-pass system has a transfer function of the form H(z) = Gz^-d, where G is a constant gain and is a constant delay d