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.

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

Sentence1: For instance, glucose is a sugar. 
Sentence2: insulin helps cells take up sugar from the blood.
sugar

Sentence1: Water is absorbed by a plant's roots. 
Sentence2: roots help plants grow.

roots