A. Activated B - cells divide to form memory cells.
Explanation:
The vaccine contains the dead version of the respective virus, so that virus will be inactive and it will become easy for the WBC to kill it and antibodies will be formed.
This is done because if we get infected by the virus, our body cells (WBC) will remember that how they killed the first entered virus (the dead version) and it will be easy for them to kill the active virus as they know the antibodies which were formed to kill the inactive virus.
