Let LRU, FIFO, and OPTIMAL represent the number of page faults in a demand$-$paged virtual memory system operating on a computer system with a main memory size of $3$ page frames, initially empty, when considering the virtual page reference string $1,2,3,2,4,1,3,2,4,1.$

a$.$

OPTIMAL $<$ LRU $<$ FIFO

b$.$

OPTIMAL $<$ FIFO $<$ LRU

c$.$

OPTIMAL $=$ LRU

d$.$

OPTIMAL $=$ FIFO