Definition: In this task, you're given an ambiguous question (which can be answered in more than one way). Your task is to write a question that clarifies the given question in such a way that the generated question has one unique answer.

Positive Example 1 -
Input: Lucifer how many episodes are in season 3?
Output: How many episodes of season 3 of Lucifer were there, including bonus episodes?

Positive Example 2 -
Input: What is the tallest ride at six flags over Texas?
Output: What is the tallest roller coaster at six flags over Texas 2001?

Negative Example 1 -
Input: Lucifer how many episodes are in season 3?
Output: How many episodes of season 4 of Lucifer were there, including bonus episodes?

Negative Example 2 -
Input: What is the tallest ride at six flags over texas?
Output: What is the tallest roller coaster at six flags over Tempe 2001?

Now complete the following example -
Input: When did coal become a major energy source?
Output: 



Output:
During what time period did coal become a major energy source globally?
When did coal first start to become a major energy source?