Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Sentence1: microscope is used to see small things by biologists by making them appear bigger. 
Sentence2: Something invented by Leeuwenhoek is used to see small things by biologists by making them appear bigger.
appear

Sentence1: if an object in a fluid is more dense than that fluid then that object will sink in that fluid because of gravity. 
Sentence2: Most seeds are more dense than water.
dense

Sentence1: Earth is a living planet. 
Sentence2: Gravity pulls objects towards Earth.

Earth