Consider two set-associative cache memory architectures: **WBC**, which uses the write back policy, and **WTC**, which uses the write through policy. Both of them use the LRU ($\textit{Least Recently Used}$) block replacement policy. The cache memory is connected to the main memory. Which of the following statements is/are TRUE?

Let us analyze each statement:

• (A) is False: In a write-back cache (WBC), when a read miss occurs and the set is full, the least recently used (LRU) block is selected as the victim. If this victim block has been modified (dirty bit is set), it must be written back to the main memory before being replaced. Therefore, a read miss in WBC can evict a dirty block.

• (B) is True: In a write-through cache (WTC), every write operation updates both the cache and the main memory simultaneously. Thus, no cache block ever remains dirty, and replacing an existing block never requires writing it back to the main memory.

• (C) is True: In WBC, when a write hit occurs on a clean cache block (dirty bit = $0$), the data in the cache is updated and its dirty bit is set to $1$. Thus, a write hit can modify the value of the dirty bit.

• (D) is False: In WTC, cache blocks are always consistent with main memory, so a victim block does not need to be written to main memory upon eviction.

Hence, statements B and C are TRUE.