= Solution
\b[A <LIFO stack> can make waiting clients starve.] Suppose client $A$ waits at the bottom of the <stack>. Before each current owner releases, a fresh client submits a request. That newest request is pushed above $A$ and is selected next. Every animation can finish promptly while $A$ waits forever.
This is <LIFO starvation>: service completion alone does not ensure <starvation freedom>. A <FIFO queue> prevents newer same-priority requests from passing $A$, whereas replacing either priority-class <FIFO queue> by a <LIFO stack> adds this problem even within one priority class. Strict priority can already starve ordinary work, as in (b); the <LIFO stack> introduces a further unfairness that can also affect urgent work.
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