For FIFO:
$\text{A}$: fault
$\text{B}$: fault
$\text{C}$: fault
$\text{D}$: fault, replaces $\text{A}$
$\text{B}$: hit
$\text{A}$: fault, replaces $\text{B}$
$\text{B}$: fault, replaces $\text{C}$
$\text{A}$: hit
$\text{D}$: hit
$\text{C}$: fault, replaces $\text{D}$
FIFO page faults = $7$.
For Clock, initially $\text{A}$, $\text{B}$ and $\text{C}$ are loaded, giving $3$ faults.
When $\text{D}$ arrives, all three reference bits are $1$.
Since the clock hand advances before checking, it moves through the pages, clears their reference bits, and eventually replaces $\text{A}$ with $\text{D}$.
Faults so far = $4$.
Next, $\text{B}$ is a hit, so its reference bit becomes $1$.
When $\text{A}$ is referenced, it is not present.
The clock advances, clears $\text{B}$'s reference bit, and replaces $\text{C}$, whose reference bit is $0$.
Faults so far = $5$.
The next references $\text{B}$, $\text{A}$ and $\text{D}$ are all hits.
Finally, $\text{C}$ is absent, producing one more fault.
Clock page faults = $6$.
For LRU:
$\text{A}$: fault
$\text{B}$: fault
$\text{C}$: fault
$\text{D}$: fault, replaces $\text{A}$
$\text{B}$: hit
$\text{A}$: fault, replaces $\text{C}$
$\text{B}$: hit
$\text{A}$: hit
$\text{D}$: hit
$\text{C}$: fault, replaces $\text{B}$
LRU page faults = $6$.
So, the correct tuple is $(7, 6, 6)$.
Answer : A
