Which of these time-steps are used to approximate the value at time-step t-\(\frac{\Delta t}{2}\) using the Crank-Nicolson scheme for finite volume approach?

Which of these time-steps are used to approximate the value at time-st

1.	Which of these time-steps are used to approximate the value at time-step t-\(\frac{\Delta t}{2}\) using the Crank-Nicolson scheme for finite volume approach?
A.	t and t+Δ t
B.	t and t-Δ t
C.	t and t-\(\frac{\Delta t}{2}\)
D.	t and t+\(\frac{\Delta t}{2}\)
Answer» C.