sentences: astronomers study celestial objects & a telescope is used for observing celestial objects by astronomers ->  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 ->  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 ->  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 ->  biologists use optical tools to observe small things  biologists use optical tools to observe small things & tool means instrument ->  biologiests use optical instruments to observe small things  astronomers use optical instruments to observe celestial objects & biologiests use optical instruments to observe small things ->  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 -> astronomers and biologists both use optical instruments to make scientific discoveries