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: if soil is permeable then water easily flows through that soil. 
Sentence2: The increase in permeability is caused by the formation and expansion of ice in the soil.

SOLUTION: permeable

PROBLEM: Sentence1: a fire requires oxygen to burn. 
Sentence2: Oxygen has  eight protons and eight electrons.

SOLUTION: oxygen

PROBLEM: Sentence1: Cancer is a disease in which cells divide out of control. 
Sentence2: Cancer is a disease which cells split and Chemotherapy stops those cells multiplying.

SOLUTION:
Cancer