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: dropping an object into water causes vibrations in the water. 
Sentence2: Dropping an object into lake causes vibrations.
[A]: dropping


[Q]: Sentence1: Oil and gasoline are fossil fuels. 
Sentence2: lawn mowers convert fossil fuels into motion.
[A]: fossil


[Q]: Sentence1: Pollen consists of tiny grains that are the male gametes of plants. 
Sentence2: Haploid plants produce gametes.
[A]:
gametes