Definition: Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Positive Example 1 -
Input: fear of needles (medically known as belomophobia) is a term used to describe a large fear (phobia) of medical procedures involving needles.
Output: fear of needles

Positive Example 2 -
Input: the 2015 ping an chinese football association super league (chinese: 2015中国平安中国足球协会超级联赛) was the 12th chinese super league season and was won by guangzhou evergrande taobao.
Output: 2015 chinese super league

Negative Example 1 -
Input: roaring lion (march 11, 2015 – august 23, 2019) was an american-bred, british-trained thoroughbred racehorse.
Output: roaring racehorse

Negative Example 2 -
Input: the maillard reaction is a chemical reaction between an amino acid and a reducing sugar that gives browned food its distinctive flavor.
Output: chemical reaction

Now complete the following example -
Input: the future of the earth will depend on many things, including increases in the brightness of the sun, loss of heat energy from the earth's core and change of the planet's orbit by the other things in the solar system.
Output: 


Output: future of the earth