According to the passage the first fire used by people was probably obtained _______.

* Hướng dẫn giải

Dẫn chứng: We do not know exactly when or how people first used fire. Perhaps, many ages ago, they found that sticks would burn if they were dropped into some hole where melted lava from a volcano lay boiling. They brought the lighted sticks back to make their fire in a cave. Or, they may have seen trees catch fire through being struck by lightning, and used the trees to start their own fires.