Gloria: Gravity is weak in Moon.
Correct: Gravity is weak on the Moon.
Explanation: The preposition "on" is used when referring to the surface of something, days and dates, a device or a machine, part of the body, and state of something.

Gloria: My weight is 42kg.
Correct: No correction.

Gloria: Gravity is strong in Earth
Correction: Gravity is strong on Earth.
Explanation: The preposition "on" is used when referring to the surface of something, days and dates, a device or a machine, part of the body, and state of something.

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Hello, Gloria! Thank you for submitting your homework.  Please do take note of the simple corrections. Have a great weekend, Gloria! Take care!.

-Teacher Isabel