Which computation represents the end-to-end response time from the user's perspective?

Which computation represents the end-to-end response time from the user’s perspective?

Compute response time uniformly as the difference between the start and finish date and time ― A to H in the diagram.

Which computation represents the end-to-end response time from the user’s perspective?
A . Sum of A to H
B. Sum of A to F
C. Sum of A, G, and H
D. Sum of A and H

Answer: D