It's a good question and imo it's not as easy to clear up as to say A or B. Short answer: The trailer contains FCS field which contains a CRC value.
The difference is hard to explain but think of it as....when a device receives a frame it will perform a Cyclic Redundant Check to see if the frame contains errors or not. If it does, it will be dropped and not forwarded out the specific switch port.
If no errors are found, it will be forwarded out the switchport towards it's destination and the CRC-value is inserted into the FCS field in the trailer. The next devices receives the frame, calculcates it's own CRC-value and compare it to the CRC value received in the FCS....and so on.
On purpose i left out how CRC is mathematically calculated as it's above my knowledge. Also a very good thing to understand is that CRC is performed to avoid 99%+ of all communication errors that occur due to noise and other interferences...but it's not guaranteed and a frame that pass the CRC-check CAN be corrupt!