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: Herbs are medicines and aids. 
Sentence2: herbs are used for curing people when they are sick.

SOLUTION: Herbs

PROBLEM: Sentence1: Macroevolution is more than repeated rounds of microevolution. 
Sentence2: evolution over geologic time above the level of the species is more than repeated rounds of microevolution.

SOLUTION: microevolution

PROBLEM: Sentence1: condensing causes a liquid to form. 
Sentence2: An example of a collective behavior is when water molecules cool and form liquid.

SOLUTION:
form