Instructions: 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.
Input: Category: THE ELEMENTS 
Clue: At its standard mass, it puts the red in red fireworks; its 90 isotope is found in nuclear fallout
Output:
strontium