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: erosion causes a river to become deeper and wider. 
Sentence2: On the contrary, the NILE is the longest river in Africa.
[EX A]: river

[EX Q]: Sentence1: dropping an object into water causes vibrations in the water. 
Sentence2: Lake water visibly disturbed.
[EX A]:
water