Answer:
D) momentum of cannon + momentum of projectile= 0
Explanation:
The law of conservation of momentum states that the total momentum of an isolated system is constant.
In this case, the system cannon+projectile can be considered as isolated, because no external forces act on it (in fact, the surface is frictionless, so there is no friction acting on the cannon). Therefore, the total momentum of the two objects (cannon+projectile) must be equal before and after the firing:

But the initial momentum is zero, because at the beginning both the cannon and the projectile are at rest:

So the final momentum, which is sum of the momentum of the cannon and of the projectile, must also be zero:

They are called <span>Frequency-modulated</span>
B- at night
In eyes of the humans, and many other animals there are two types of receptors, the rods, and the cones. The cones have an important role in color vision and they possess different types of pigment which enable color vision.
On the other hand, the rods are more sensitive to light, and they are responsible for black and white vision.
Therefore, an increase in the number of rods can enable the animal to see betther in the dark.
The force of gravity will change the satellites direction, and therefore its velocity. To complete the sentence "<span>The force of gravity is responsible for continuously changing the velocity of a satellite." Thank you for posting your question here at brainly. I hope it helps. </span>