Header of a frame generally containsa.synchronization bytesb.all of the mentionedc.frame identifierd.addresses

The header of a frame generally contains:

a. Synchronization bytes: These are used to indicate the start of a new frame. They help the receiver to identify the start of a new packet of data.

b. All of the mentioned: This option suggests that the header of a frame contains all the elements mentioned in the other options.

c. Frame identifier: This is a unique identifier for each frame. It helps in distinguishing between different frames in a sequence.

d. Addresses: These are the source and destination addresses. They indicate where the frame is coming from and where it is supposed to go.

So, the header of a frame generally contains all of the mentioned elements: synchronization bytes, frame identifier, and addresses.