RULE: Before coupling cars, train operators must see that the brake is set up on the section to which coupling is to be made. When making coupling on grade, they must move cars upgrade: The principle safety feature realized by coupling upgrade is that the
a. coupler on the stationary section is centered because it hangs down
b. train is less likely to roll backward
c. braking force is evenly distributed
d. coupler is less likely to malfunction