The answer for the online test is going to be the last one, D
Answer: option A. strong nuclear force.
Explanation:
The diagram shows the subatomic particles inside the nucelous: protons and neutrons.
As you know, the protons are positively charged partilces inside the nucleous.
Being those particles charged with the same kind of charge they experiment electrostatic repulsion. So, how do you explain that they can stand together in such small space as it is the nucleous?
The responsible of keeping the subatomic particles together is the so called strong nuclear force.
Strong nuclear force or simply strong force is one of the four fundamental interactions or forces: i) gravitational, ii) electromagnetic, iii) weak nuclear force, and iv) strong nuclear force.
Strong nuclear force is the strongest force of nature and acts only in short distances as those inside the nucleous and is responsible for both the atraction among quarks and the atraction among protons to bind them together inside the atomic nucleous.
Answer:
The distance is 55.636 billion miles, or 528.2 AU.
Explanation:
Since the distance from the Sun to Neptune is 2.7818 billion miles, the distance from the Sun to Planet Nine would be 20 times that, which is:

or 55.636 billion miles.
Since 1 astronomical unit (AU) is 93 million miles, that distance is also:

In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture.