Detailed Instructions: Based on the information present in the given passage, you need to write a correct answer to the given question. A correct answer is one that correctly and completely answers the question. Do not write answers that address the question partially or incorrectly. The correct answer must be contained in the given paragraph.
Problem:Paragraph- Sent 1: Imagine you are standing in a farm field in central Illinois.
Sent 2: The land is so flat you can see for miles and miles.
Sent 3: On a clear day, you might see a grain silo 20 miles away.
Sent 4: You might think to yourself, it sure is flat around here.
Sent 5: If you drive one hundred miles to the south, the landscape changes.
Sent 6: In southern Illinois, there are rolling hills.
Sent 7: Why do you think this is?
Sent 8: What could have caused these features?
Sent 9: There are no big rivers that may have eroded and deposited this material.
Sent 10: The ground is capable of supporting grass and trees, so wind erosion would not explain it.
Sent 11: To answer the question, you need to go back 12,000 years.
Sent 12: Around 12,000 years ago, a giant ice sheet covered much of the Midwest United States.
Sent 13: Springfield, Illinois, was covered by over a mile of ice.
Sent 14: Its hard to imagine a mile thick sheet of ice.
Sent 15: The massive ice sheet, called a glacier, caused the features on the land you see today.
Sent 16: Where did glaciers go?
Sent 17: Where can you see them today?
Sent 18: Glaciers are masses of flowing ice. 
Question: How long ago was Springfield, Illinois covered by over a mile of ice?.
Solution:
Around 12,000 years ago.