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Two Writes Out Of Four

A machine has three physical frames and uses strict LRU replacement. All pages start out of memory. The access trace is:

step access page operation
1 read A load
2 read B load
3 write C store
4 read A load
5 write D store
6 read C load
7 read E load
8 write B store
9 read A load

The OS writes an evicted page back to swap only when its dirty bit is set. How many disk writes does this trace cause?