Most people can survive only a few days without what?
Options:
- (A) carbon dioxide
- (B) oxygen
- (C) h2o
- (D) H20
- (E) NaCl
- (F) CO2
- (G) soda
- (H) urea
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Let's think first: Most people can survive only a few days without water. Water is everywhere H20. Most people can survive only a few days without H20.... So the answer is [(D)]

A parasites that can kill is called what?
Options:
- (A) bacteria
- (B) a carcinogen
- (C) A Greek letter
- (D) a pathogens
- (E) animals
- (F) an infection
- (G) insects
- (H) dangerous
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Let's think first: Some parasites kill their host, but most do not. Pathogens induce a disease in their host. Some parasites that kill are called pathogens, but most do not.... So the answer is [(D)]

Starfish, sea urchins and sea cucumbers lack a what?
Options:
- (A) characteristics
- (B) the body's largest organ
- (C) watery habitat
- (D) centralized nervous system
- (E) functioning arm
- (F) underwater life
- (G) biological diversity
- (H) epidermis and dermis
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Let's think first: Echinoderms lack a centralized nervous system. Echinoderms include starfish, sea urchins, and sea cucumbers. Starfish, sea urchins and sea cucumbers lack a centralized nervous system.... So the answer is [(D)]