A) The deadliest form of the plague is commonly known as the "Black Death" or "Bubonic Plague". It is estimated to have killed between 75 to 200 million people in Eurasia during the 14th century.
B) The Bubonic Plague primarily attacks the lymphatic system of the human body. It is caused by the bacterium Yersinia pestis and is transmitted through the bites of infected fleas. The bacteria travel through the bloodstream and infect the lymph nodes, causing them to become swollen and painful. Other symptoms include fever, chills, and weakness. If left untreated, the disease can be fatal.