The answer is **A. Campylobacter**.
Campylobacter jejuni is a bacterium that causes diarrhea. It is the most common infectious trigger of Guillain-Barré syndrome (GBS), a rare neurological disorder that causes muscle weakness and paralysis.
The other microorganisms listed in the question (E. coli, Salmonella, and Shigella) are also associated with diarrhea, but they have not been as strongly linked to GBS.
It is important to note that GBS can also be triggered by other factors, such as viral infections and vaccinations. However, infection with Campylobacter jejuni is the most common known trigger.
If you have recently had diarrhea and are experiencing muscle weakness or paralysis, it is important to see a doctor right away. GBS is a serious condition, but it is usually treatable.