TASK DEFINITION: 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.
PROBLEM: Sentence1: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.

SOLUTION: a

PROBLEM: Sentence1: Speciation events are thus examples of macroevolution. 
Sentence2: Speciation events occur over geologic time above the level of the species.

SOLUTION: Speciation

PROBLEM: Sentence1: waxy leaves are used for storing water by some plants. 
Sentence2: leaves are used to store water.

SOLUTION:
storing