_ is found in most molecules.
Options:
- (A) glucose
- (B) Gold
- (C) Energy
- (D) food
- (E) Polonium
- (F) Nitrogen
- (G) Helium
- (H) heat energy
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Let's think first: Nitrogen is found in proteins, nucleic acids, and chlorophyll. Most molecules are proteins or nucleic acids. Nitrogen is found in most molecules.... So the answer is [(F)]

What has a centralized nervous system with a brain?
Options:
- (A) Man
- (B) Birds
- (C) leeches
- (D) shark
- (E) evergreens
- (F) salmon
- (G) worms
- (H) pan
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Let's think first: Fish have a centralized nervous system with a brain. Sharks are a type of fish. Sharks have a centralized nervous system with a brain.... So the answer is [(D)]

What do organisms cluster around, in the ocean floor?
Options:
- (A) cracks
- (B) chemicals
- (C) limestone
- (D) crust
- (E) headaches
- (F) Nutrients
- (G) horses
- (H) dogs
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Let's think first: Organisms cluster around hydrothermal vents in the ocean floor. Background Hot water vents form inside cracks in the ocean floor. Organisms cluster around cracks in the ocean floor.... So the answer is [(A)]

What has a characteristic life cycle that includes alternation of generations?
Options:
- (A) humans
- (B) leaves
- (C) Oak
- (D) dogs
- (E) Trees
- (F) cacti
- (G) amoeba
- (H) ferns
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Let's think first: All plants have a characteristic life cycle that includes alternation of generations. All ferns are shade plants. Ferns have a characteristic life cycle that includes alternation of generations.... So the answer is [(H)]

What group of animals are a tetrapod vertebrate that produce amniotic eggs?
Options:
- (A) class Reptilia
- (B) warm-blooded
- (C) more abundant
- (D) graptolites
- (E) animals
- (F) insects
- (G) mammals
- (H) barnacles
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Let's think first: Reptiles are a class of tetrapod vertebrates that produce amniotic eggs. Reptilia contains over 7800 entries on numerous species of reptiles. Animals in the class Reptilia are a class of tetrapod vertebrates that produce amniotic eggs.... So the answer is [(A)]

How are atolls built?
Options:
- (A) important habitats
- (B) By coral exoskeletons
- (C) by fish
- (D) with machines
- (E) by a type of eel
- (F) It used to be covered by water
- (G) The area was once underwater
- (H) reusing materials
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Let's think first: Many corals secrete an exoskeleton that builds up to become a coral reef. An atoll is the third type of reef. Atolls are built by corals secreting an exoskeleton.... So the answer is [(B)]