Answer: B. A gravitational field
Explanation:
Surrounding earth is gravitational field. Gravitational field is a region of space were gravitational force can be felt and gravitational force is the gravitational pull on the surface of the earth. The presence of this gravity is what allow us to be able to walk freely without falling. It also make us jump up and be able to land back on the ground. Assuming there are no force of gravity in the surface of the earth, there won't be any possibility of landing back on the ground after jumping.
The answer is the letter a
The atoms of some materials have no free electrons in their outer orbits. These electrons are busy doing other jobs, like being shared in the orbits of two adjacent atoms. They are so closely held that it is very difficult to pull them away. Most compounds of carbon and hydrogen are like this.
<span>Plastics, whose molecules are made from long combinations of carbon and hydrogen atoms, have few or no free electrons. This means that plastics are poor conductors of electricity (and they are also poor conductors of heat). hope that helped.</span>
Let's start from the Fluorine (F), which has 4 atoms on the right side: this means we must put a factor 4 in front of HF to balance the number of atoms of Fluorine.
Nowe we have 4 atoms of hydrogen, H, on the left side. Since we have a

on the right side (2 atoms), we must put a factor 2 in front of

, to balance the number of atoms of hydrogen.
So now the atoms of oxygen are also balanced (2 on both sides), as well as the atoms of Silicon (Si), so the balanced reaction is