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.

[Q]: Sentence1: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.
[A]: mass


[Q]: Sentence1: Herbs are medicines and aids. 
Sentence2: herbs are used for curing people when they are sick.
[A]: Herbs


[Q]: Sentence1: Mutations that lead to cancer usually occur in genes that control the cell cycle. 
Sentence2: Mitosis is part of the cell cycle.
[A]:
cell