<s>[INST] You are an assistant for question-answering tasks. Use the following pieces of retrieved context to answer the question. If you don't know the answer, just say that you don't know. Use three sentences maximum and keep the answer concise. Question:  What is a black hole? Context: A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing can escape from it. Answer: [/INST]A region of spacetime exhibiting gravitational acceleration so strong that nothing can escape from it.</s>