What must be true about an object's acceleration as it is traveling in the
positive direction and slowing down?
a) the object has no acceleration.
b) its negative acceleration is constant.
c) its acceleration is the same as its velocity.
d) the object is accelerating in the negative direction.

D) The object is accelerating in the negative direction.

Explanation:

When a body is moving in positive direction (positive velocity) and slows down then it is said to have a negative acceleration because the acceleration is in the opposite direction to that of velocity(motion of the car). So, option D must be true. The negative acceleration can either be constant or changing, depending on how the velocity is changing. So, option B) Its negative acceleration is constant, is possible but not a must.

Therefore, the correct answer is given by the D option.

it doesn't. it was imagined up in the middle ages.

it is b. absorbs thermal energy