instruction:
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: Lymph is a fluid that leaks out of capillaries into spaces between cells. 
Sentence2: Humans are made up of trillions of cells.
answer:
cells


question:
Sentence1: a battery converts chemical energy into electrical energy. 
Sentence2: A battery produces a flow of electrons.
answer:
battery


question:
Sentence1: the number of rings in a tree trunk can be used to estimate the age of the tree. 
Sentence2: Tree rings are examined to learn the forest age and growth rate.
answer:

age