The answer is; A
Since the earth was formed approximately 4.6 billion years ago, the heat that was generated during its formation has not been entirely lost. Some of the heat is still insulated inside the earth (below the crust) and is only lost very slowly over time. In addition, the earth hardly cools because the lost heat is replenished by the heat from radioactive elements that decay in the earth’s core. Some of these radioactive elements are uranium.
