Answer:
D. Speed up the assembly line transfer mechanism
Explanation:
All of the options are logic and very intelligent ways to reduce the longest task time, but if you just speed up the assembly line transfer you will end up with two possible outcomes, frustrated workers cause they always have to be rushing up to finish their task and thus a lower quality in the product you are producing, or that the workers on that specific part of the assembly line definetely can´t perform the task and endu up not doing their job and you end up with incomplete products.