TASK DEFINITION: In this task, you're given an open-domain question. Your task is to provide an answer to the given question. There is only one unique answer for each question. Your answer should be short, and refer to an entity, date, number, etc. Do not put your answer in the context of a sentence.
PROBLEM: What is the si unit of time period?

SOLUTION: second

PROBLEM: How are point sources of pollution regulated by the cwa?

SOLUTION: requires dischargers to obtain a National Pollutant Discharge Elimination System (NPDES) permit

PROBLEM: When was the horse and his boy written?

SOLUTION:
September 6, 1954