- Astronomers study celestial objects
- A telescope is used for observing celestial objects by astronomers
- So, astronomers use telescopes to observe celestial objects

- Astronomers use telescopes to observe celestial objects
- A telescope is a kind of optical instrument for observing celestial objects
- Therefore, astronomers use optical instruments to observe celestial objects

- A microscope is used to see small things by making them appear bigger
- Biologists study small things such as cells
- Therefore, biologists use micropscopes to see small things

- Biologists use micropscopes to see small things
- A microscope is a kind of optical tools for observing small things
- Hence, biologists use optical tools to observe small things

- Biologists use optical tools to observe small things
- Tool means instrument
- Hence, biologiests use optical instruments to observe small things

- Astronomers use optical instruments to observe celestial objects
- Biologiests use optical instruments to observe small things
- So, astronomers and biologists both use optical instruments to make observations

- Astronomers and biologists both use optical instruments to make observations
- Making scientific discoveries requires observing
- Hence, astronomers and biologists both use optical instruments to make scientific discoveries

So, astronomers and biologists both use optical instruments to make scientific discoveries
Astronomers and biologists study different areas of science. Many astronomers observe far distant objects in the sky. Many biologists study extremely small objects. What do these astronomers and biologists have most in common?
- A microscope is a kind of optical tools for observing small things 
- A microscope is used to see small things by making them appear bigger 
- Biologists study small things such as cells 
- A telescope is a kind of optical instrument for observing celestial objects 
- Tool means instrument 
- Making scientific discoveries requires observing 
- Astronomers study celestial objects 
- A telescope is used for observing celestial objects by astronomers