Definition: In this task, you need to write a topic word from the given fact. The topic word must have at least one word overlap with the given fact. The topic word often involves adding a new word from a related concept. In your topic word, use at least one word from the given fact. Topic words with two or more words work best.

Positive Example 1 -
Input: Fact: pesticides cause pollution.
Output: pollution harms.

Positive Example 2 -
Input: Fact: pesticides cause pollution.
Output: modern farming pesticide.

Negative Example 1 -
Input: Fact: pesticides cause pollution.
Output: computer harms.

Negative Example 2 -
Input: Fact: pesticides cause pollution.
Output: toopaste helps.

Now complete the following example -
Input: Fact: most canyons are formed by flowing rivers through erosion over long periods of time.
Output: 


Output:
Erosion is.
canyon columbia river gorge.
canyon deep gorge.
canyon deep.
canyon erosion river.
canyons form.
erosion is weathering.
erosion.
river erosion.
river water.
rivers contain water.
rivers flows due to.
striation erosion river.
water erosion.