Question: Just a few days ago, Beth waded into her family's pond. Now when she stepped off the bank the pond was hard and she could walk on the surface. What happened?

  Options: 
 A. a cold front had moved into the area
 B. The pond had drained into an underground river
 C. There was a lot of algae on the pond's surface
 D. It had rained the night before
Answer: A