Galileo was an Italian astronomer who:
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Developed the telescope
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Discovered 4 satellites of Jupiter
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Discovered that the movement of the pendulum produces a regular time measurement
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All are correct
Galileo Galilei is famous for developing improved telescopes (he didn't invent the telescope), discovering Jupiter's four largest moons (the Galilean satellites), and studying pendulum motion for time measurement. 'All are correct' is accurate because Galileo contributed to all three areas, though the telescope claim requires qualification.
Galileo Galilei made multiple landmark contributions to science: he built and improved the telescope for astronomical observation, discovered the four largest moons of Jupiter (the Galilean moons), and studied the pendulum's isochronism, showing it could be used to measure time regularly. Since all three statements are individually true, "All are correct" is the right choice.