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: a stopwatch is used to measure time. 
Sentence2: Time can be measured with a clock or watch.

SOLUTION: measure

PROBLEM: Sentence1: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.

SOLUTION: fertilization

PROBLEM: Sentence1: lakes are formed by precipitation and runoff. 
Sentence2: bodies of water are formed by numerous events.

SOLUTION:
formed