Answer:
d. vehicle balance
Step-by-step explanation:
One aspect motorists need to do constantly is to maintain a optimum vehicle balance, otherwise they would fall.
Actually, when they turn in corners, they don't decreases their velocity too much, what they do is to modify their posture, to apply breaks and accelration at specific moments, that will ensure a perfect turn without losing too much velocity.
Therefore, the right answer is d. vehicle balance.