Newtons first law states that an object will remain still or in straight line. Until acted upon some force!
Answer: B. a stream of particles
The light is said to travel in a straight line and casts a shadow therefore, Isaac Newton formulated a hypothesis stating that lights is a stream of particles. This theory is later called the Corpuscular theory of light.
Since Astronaut and wrench system is isolated in the space and there is no external force on it
So here momentum of the system will remain conserved
so here we can say

initially both are at rest
so here plug in all values


so here the astronaut will move in opposite direction and its speed will be equal to 0.20 m/s
For the most part aesthetics but you could argue they reduce air turbulence in some cases which would lead to better gas mileage. On sports cars however the goal is usually down force which is not wanted on economy cars as it can actually worsen gas mileage.
I hope that answered your question.
The dens or the odontoid process of the axis or the second cervical spine forms a pivot point with the atlas or the first cervical vertebrae that is responsible for the nodding and the rotational movements of the head. This is reinforced by ligaments and the atlanto-occipital joint that allows the head to make a nodding or up and down movement on the vertebral column.