Detailed 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.
Q: Category: MEASURE FOR MEASURE 
Clue: In viscosity ratings, the "W" in 10W-40 means 10 is the winter grade rating of this liquid
A:
motor oil