Teacher: You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Category: HOMOPHONIC PAIRS 
Clue: It's a notation on a percussion store to clash
Solution: cymbal symbol
Reason: "Cymbal" and "symbol" both have the same pronunciations but different meanings, hence they are homophonic pairs. A symbol is the notation and a cymbal is a percussion instrument that clashes and rings.

Now, solve this instance: Category: MODERN MATERIALS 
Clue: Introduced in the '70s to replace steel belting on high-speed tires, it's called stronger than steel & lighter than nylon
Student:
kevlar