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.

[EX Q]: Sentence1: Lymphocytes are the key cells involved in the immune response.
Sentence2: The key cells involved in the immune response produce antibodies.
[EX A]: cells

[EX Q]: Sentence1: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past.
Sentence2: Fossils are the remains of prehistoric life.
[EX A]: fossils

[EX Q]: Sentence1: Roots have primary and secondary meristems for growth in length and width.
Sentence2: Special types of primary roots are tap roots or turnips.
[EX A]:
Roots