Jupiter came close to Earth during his lifetime. He realized that all of the planets go around the Sun. He invented advanced tools for looking at the sky. Earlier scientists failed to take an interest in the sky.
I gave my students this multiple choice question: What enabled Galileo in the 17th century to see the moons of Jupiter?

Only one answer is correct among these 4 choices:
- Jupiter came close to Earth during his lifetime.
- He realized that all of the planets go around the Sun.
- He invented advanced tools for looking at the sky.
- Earlier scientists failed to take an interest in the sky.

Could you tell me which one is correct?

He invented advanced tools for looking at the sky.