Final answer:
The venom of a black widow spider primarily affects the nervous system, causing symptoms like pain, muscle cramps, and nausea, which typically last from 3 to 7 days. The correct option is b.
Step-by-step explanation:
The venom of a black widow spider is particularly toxic to the nervous system. The main component of the venom, latrotoxins, alongside other compounds like polypeptides, adenosine, and guanosine, disrupt normal nervous system function. This can cause a range of symptoms including pain and sweating at the bite location, muscle cramps, headache, nausea, vomiting, and weakness. The symptoms typically persist for 3-7 days following the bite. It is important to note that only the female black widow's bite poses a significant danger to humans due to the larger venom glands they possess.