An access sequence of cache block addresses is of length $N$ and contains $n$ unique block addresses. The number of unique block addresses between two consecutive accesses to the same block address is bounded above by $k$. What is the miss ratio if the access sequence is passed through a cache of associativity $A \ge k$ exercising least-recently-used replacement policy?

Since the cache has associativity $A \ge k$ and uses the LRU (Least Recently Used) replacement policy, a block will remain in its set as long as fewer than $A$ distinct blocks mapping to the same set are accessed between two successive references to it.

Between any two consecutive accesses to the same block address, at most $k$ unique block addresses are accessed across the entire sequence (and hence at most $k \le A$ in the same set). Therefore, after the very first reference (cold/compulsory miss) to each of the $n$ unique block addresses, that block will never be evicted before its next access. Every subsequent access to that block will result in a cache hit.

Thus:

• Total number of misses = Number of compulsory misses = $n$

• Total number of accesses = $N$

Hence, option (A) is correct.