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: a rainbow is formed by refraction of light by separating light into all different colors.
Output: 


Output:
Refraction.
colors wavelengths.
light rays.
light refract water.
light refraction prism.
light refraction.
prism refraction.
rainbow refract.
rainbow spectrum.
rainbow.
rainbows diffraction.
water vapor light.