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: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: If you place gas in an open box it will evaporate and spread out into the air.

SOLUTION: gas

PROBLEM: Sentence1: freezing means changing from a liquid into a solid by reducing heat energy. 
Sentence2: Water freezes into ice when cooled.

SOLUTION: freezing

PROBLEM: Sentence1: Roots have primary and secondary meristems for growth in length and width. 
Sentence2: Special types of primary roots are tap roots or turnips.

SOLUTION:
Roots