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: high mountains with well-rounded peaks can be formed by collision of crustal plates. 
Sentence2: high mountains with well-rounded peaks can be formed by collision of plate tectonics.

SOLUTION: collision

PROBLEM: Sentence1: Runoff water is wasted water. 
Sentence2: Streams may start with wasted water.

SOLUTION: wasted

PROBLEM: Sentence1: Some precipitation that falls on land may soak into the ground, becoming groundwater. 
Sentence2: Springs can be fed from precipitation that soaks into the ground.

SOLUTION:
ground