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.

[EX Q]: Sentence1: a circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.
[EX A]: circle

[EX Q]: Sentence1: Spikes are forceful the tidal waves of electric current. 
Sentence2: spikes come from tidal energy.
[EX A]: Spikes

[EX Q]: Sentence1: When the magma cools and hardens, it turns into igneous rock. 
Sentence2: magma turns into igneous rocks.
[EX A]:
igneous