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.

Q: Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

A: Smoking
****
Q: Sentence1: If there is an increase in UV radiation, the risks go up for all types of skin cancer. 
Sentence2: Ozone depletion increases the risks for all types of skin cancer.

A: all
****
Q: Sentence1: Limestone caves displaying stalactites. 
Sentence2: Limestone caves are formed by depositions.

A:
Limestone
****