For the 747 the answer would be a
for the 744 it would be b

emg brakes
 

B707 had emg brakes, if the hydraulic fluid systems failed.
emg brakes consisted of a compressed gas bottle, a valve and handle on captains panel.
When valve operated compressed gas was introduced into the hydaulic pipes to the wheel brakes and operated the pistons just like fluid.
there was no differential braking braking.
the brakes had to be bled afterwards, which was better than digging the plane out of the boundry fence.