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.
--------
Question: Sentence1: a stopwatch is used to measure time. 
Sentence2: Time can be measured with a clock or watch.

Answer: measure


Question: Sentence1: Energy enters ecosystems in the form of sunlight or chemical compounds. 
Sentence2: Energy enters ecosystems in the form of photons.

Answer: Energy


Question: Sentence1: Bottleneck effect occurs when a population suddenly gets much smaller. 
Sentence2: Genetic variation can be reduced by random genetic drift, population bottlenecks, founder effect.

Answer:
Bottleneck