Question

the immune system protects the body against disease - causing organisms like viruses, bacteria, fungi, and parasites. there are different stages of the immune systems response. first, your skin and the mucus in your respiratory tract and the acid in your stomach, can kill pathogens. if that doesnt work, your white blood cells swallow and break down invaders. inflammation or a fever are signs that your immune system is in the midst of a fight against pathogens.
the lymphatic system also plays a huge role in defending the body against germs. its job is to help keep the level of fluid (called lymph) in the body balanced, as well as to drain it from the body. lymph nodes filter lymph fluid, and most are found in clusters in the neck, armpit and groin. when they detect foreign invaders during the filtering process, they manufacture more lymphocytes (a kind of white blood cell), causing the nodes to swell.
according to the passage, when lymph nodes swell, it is often a sign that
choose one option
a your skin fought off pathogens that tried to enter your body.
b your body is fighting against germs that it thinks are invaders.
c your level of lymph is low and so the body is working hard.
d your body is not producing enough lymphocytes.

Explanation:

The passage states that lymph nodes filter lymph fluid and during filtering, they manufacture more lymphocytes (white blood cells) when fighting foreign invaders, causing swelling. This directly links swollen lymph nodes to the body fighting germs/invaders. Option A refers to skin (not lymph nodes), C mentions low lymph (no such link in text), D claims insufficient lymphocytes (opposite—nodes make more). Thus B is correct.

Answer:

B. your body is fighting against germs that it thinks are invaders.