Which of the following statements is correct regarding the proof of work consensus model? A. Adjusting the difficulty target helps ensure that no entity can take over block production and to avoid the formation of multiple sub-chains. B. When using the proof of model, Bitcoin system can add the numbers of leading zeros decrease the difficulty of solving the puzzle. C. A common puzzle method is to require that the hash digest of a block header be equal to a target value. D. All the above are correct. E. None of the above is correct