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: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.
[A]: a


[Q]: Sentence1: Flies are insects with two wings. 
Sentence2: Flies are arthropods with two wings.
[A]: Flies


[Q]: Sentence1: Male gametes are called sperm. 
Sentence2: Male gametes are released into the surrounding water through the osculum.
[A]:
Male