Task: Question Understanding
Input (English): Question: Obsidian is an igneous rock that looks very smooth, like glass. Which statement BEST describes how obsidian forms? (A) magma or lava erodes very slowly (B) magma or lava erodes very quickly (C) magma or lava cools and hardens slowly (D) magma or lava cools and hardens quickly?
Output (English): BEST, describes, obsidian, forms?