In 1687, explained that gravitational forces hold the solar system together.
a. newton
c. halley
b. copernicus
d. galileo

   A. Isaac Newton

Explanation:  Isaac Newton (1643 - 1727) was one of the greatest geniuses among scientists of all time, known for his laws of motion and theory of gravity. According to his theory, gravity holds all the bodies in the earth's atmosphere, so it is applicable on earth, but it is also applicable in the cosmos. Since all celestial bodies circle around the sun on exactly defined paths and in the same time period, gravity together with the force of inertia is the one that maintains the perfect order in the solar system.

answer: ensure protection from communism

explanation:

the north atlantic treaty was largely dormant until the korean war initiated the establishment of nato to implement it, by means of an integrated military structure: this included the formation of supreme headquarters allied powers europe in 1951, which adopted the western union's military structures and plans.