To understand Newton's 1st law. Newton's Principia states this first law of motion: An object subject to no net force maintains its state of motion, either at rest or at constant speed in a right line. This law may be stated as follows: If the sum of all forces acting on an object is zero, then the acceleration of that object is zero. Mathematically this is just a special case of the 2nd law of motion, F =ma , when F =0. When studying Newtonian mechanics, it is best to remember the 1st law in two ways: If the net force (i.e., sum of all forces) acting on an object is zero, the object will keep moving with constant velocity (which may be zero). If an object is moving with constant velocity, that is, with zero acceleration, then the net force acting on that object must be zero.
Part A
If a car is moving to the left with constant velocity, one can conclude that ?
(a) there must be no forces applied to the car.
(b) the net force applied to the car is directed to the left.
(c) the net force applied to the car is zero.
(d) there is exactly one force applied to the car.
Part B
An object cannot remain at rest unless

(a) there are no forces at all acting on it.
(b) the net force acting on it is zero.
(c) the net force acting on it is constant.
(d) there is only one force acting on it.
Part C

An object will have constant acceleration if?
(a)there are no forces at all acting on it.
(b)the net force acting on it is zero.
(c)the net force acting on it is constant in magnitude and direction.
(d)there is only one force acting on it.

If a car is moving to the left with constant velocity, the change in velocity of the car is equal to zero. So the acceleration of the car is zero. As a result, the the net force applied to the car is zero.

So, the correct option is (c) "the net force applied to the car is zero".

Part B,

An object cannot remain at rest unless the net force acting on it is zero. This is Newton's first law of motion.

So, the correct option is (b).

Part C,

An object will have constant acceleration, the net force acting on it is constant in magnitude and direction. The net force acting on the object is directly proportional to its acceleration.

So, the correct option is (c).

Hence, this is the required solution.