The pet store has T$1$ which occurs at $3$:$45$pm while T$2$ & T$3$ occur at $5$:$00$pm to $6$:$00$pm$.$ The system crashes at $6$:$45$pm during T$4.$ You perform recovery $\_\_\_\_\_\_\_\_\_$ to restore the data that occurred before T$4.$

a$.$

rollback

b$.$

immediate update

c$.$

database checkpoint

d$.$

deferred$-$ write technique