Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: The first period of the Paleozoic Era was the Cambrian. By the beginning of the Paleozoic, organisms evolved shells. Shells could hold their soft tissues together. Shells could protect them from predators and from drying out. Some organisms evolved external skeletons. These are called exoskeletons . Organisms with hard parts also make good fossils. Fossils from the Cambrian are much more abundant than fossils from the Precambrian. Answer: cambrian

Answer: The first period of the paleozoic era was called what?

Question: Passage: Blood Blood is considered a connective tissue because it has a matrix, as shown in Figure 33.17. The living cell types are red blood cells (RBC), also called erythrocytes, and white blood cells (WBC), also called leukocytes. The fluid portion of whole blood, its matrix, is commonly called plasma. Answer: connective

Answer: What type of tissue is blood?

Question: Passage: Encephalitis and meningitis aren't very common, but they can be extremely serious. They may cause swelling of the brain, which can be fatal. That's why it's important to know the symptoms of these diseases. Both encephalitis and meningitis typically cause a severe headache and a fever. Meningitis also causes a stiff neck. Both require emergency medical treatment. Answer: brain

Answer:
Fatal swelling of what organ can result from both encephalitis and meningitis, which typically cause a severe headache and a fever?