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: Diurnal cycles Diurnal cycles are the daily cycles of light and darkness. 
Sentence2: Plants detect and respond to diurnal cycles.

SOLUTION: Diurnal

PROBLEM: Sentence1: propulsion is used for flying by a spacecraft. 
Sentence2: When Apollo 12 took off, the spacecraft was hit by lightning.

SOLUTION: spacecraft

PROBLEM: Sentence1: The results of a planet's rotation is its length of day. 
Sentence2: a planet has cycles caused by rotation.

SOLUTION:
rotation

