Astronomy is the oldest science known to man. Thousands of years ago man looked at the stars and wondered about the heavens. But man was limited by what he could see with his eyes alone. The Greeks studied astronomy over 2,000 years ago. They could see the size, color, and brightness of a star. They could see its place in the sky. They watched the stars move as the seasons changed. But the Greeks had no tools to help themselves study the heavens. Each new tool added to the field of astronomy helped man reach out into space. They did not know that the planet called Saturn  had rings around it. Their sight was so limited that they could not see all the planets. In the early 1700s, people thought there were only six planets. Nepture , the last of eight planets to be discovered, was not seen until 1846. Before the spectroscope , man did not know what kind of gases was in the sun or other stars. Without the radio telescope, we didn't know that radio noises came from far out in space. Today, astronomy is a growing science. We had learned more in the last fifty years than in the whole history of astronomy. . This passage mainly talks about   _  .
tools used in astronomy the development of astronomy in the last 50 years Greeks' achievements in astronomy new tools and the development of astronomy
Question: Astronomy is the oldest science known to man. Thousands of years ago man looked at the stars and wondered about the heavens. But man was limited by what he could see with his eyes alone. The Greeks studied astronomy over 2,000 years ago. They could see the size, color, and brightness of a star. They could see its place in the sky. They watched the stars move as the seasons changed. But the Greeks had no tools to help themselves study the heavens. Each new tool added to the field of astronomy helped man reach out into space. They did not know that the planet called Saturn  had rings around it. Their sight was so limited that they could not see all the planets. In the early 1700s, people thought there were only six planets. Nepture , the last of eight planets to be discovered, was not seen until 1846. Before the spectroscope , man did not know what kind of gases was in the sun or other stars. Without the radio telescope, we didn't know that radio noises came from far out in space. Today, astronomy is a growing science. We had learned more in the last fifty years than in the whole history of astronomy. . This passage mainly talks about   _  .
A. tools used in astronomy
B. the development of astronomy in the last 50 years
C. Greeks' achievements in astronomy
D. new tools and the development of astronomy
Answer: