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: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.
answer:
egg


question:
Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: molds are antigens.
answer:
antigen


question:
Sentence1: Deltas are typical on coastlines with large rivers. 
Sentence2: rivers will fan out and deposit sediment typically near a coastline.
answer:

coastlines