Step 1: Carriers are classified by how and when they harbour the organism. The defining twist of a paradoxical carrier lies in the source of acquisition.
Step 2: The paradox is that the organism is picked up not from a sick patient but from another carrier - someone who themselves shows no disease. That uniquely matches choice (b).
Step 3: Acquiring it from a patient (option a) is ordinary contact transmission, and the convalescent carrier (option c) is one who has recovered yet still sheds the agent. Both are different carrier concepts, so they are excluded.
\[\boxed{\text{A person who acquires the microorganism from another carrier}}\]