_ bind to allergens.
Options:
- (A) to stay warm
- (B) mammals
- (C) fur and fat
- (D) animals
- (E) protect them
- (F) Most plants
- (G) Antibodies
- (H) Chemical energy
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Let's think first: Antibodies are large, Y-shaped proteins that recognize and bind to antigens. Allergens are also called Antigens. Antibodies bind to allergens.... So the answer is [(G)]

What feature allows frogs to absorb substances from the environment?
Options:
- (A) four limbs
- (B) poison dart frog
- (C) hydrate their cells
- (D) permeable skin
- (E) layers of fat
- (F) a cuticle
- (G) predators
- (H) double eyelid
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Let's think first: Amphibians have permeable skin that easily absorbs substances from the environment. All frogs are amphibians. Frogs have permeable skin that easily absorbs substances from the environment.... So the answer is [(D)]

Where do all adult echinoderms live?
Options:
- (A) soil
- (B) desert
- (C) freshwater
- (D) fossils
- (E) water
- (F) Earth
- (G) small
- (H) aquariums
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Let's think first: Adult echinoderms have radial symmetry. All animals with radial symmetry live in water. All adult echinoderms live in water.... So the answer is [(E)]