To assign buffers to a DCB (Data Control Block), you can use the BUFNO subparameter.
The BUFNO subparameter specifies the number of buffers to be assigned to the DCB. Buffers are temporary storage areas that hold data temporarily during input/output operations. By assigning buffers to a DCB, you can enhance the performance of input/output operations by reducing the number of physical I/O operations to the external storage.
Therefore, the correct answer is:
D) Through the BUFNO subparameter