The knowledge point examined in this question is the basic knowledge of information system security.

In the process of digital signature, asymmetric encryption algorithm is adopted. One pair of keys (public key and private key) is used for encryption, and the other pair is used for decryption. Therefore, if the sender uses his own private key for encryption, the receiver uses the sender's public key for decryption. This question A is the sender and B is the receiver. So the answer is B.