q: What does the substance that male dogs have in urine to mark their territory do?
Options:
- (A) sweating
- (B) attract females
- (C) Release energy
- (D) repels females
- (E) attract enemies
- (F) attract males
- (G) adding heat
- (H) dangerous
a: (B)... Explanation: Male dogs use pheromones in urine to mark their territory. Males produce 'pheromones' to attract females. Male dogs use something that attracts females in urine to mark their territory. That's why the answer is (B).

q: Many corals secrete what to form a coral reef?
Options:
- (A) Chlorophyll
- (B) salt and water.
- (C) The area was once underwater
- (D) Chemical energy
- (E) aqueous solution
- (F) Organic compounds
- (G) gastropod shells
- (H) hard outer covering
a: (H)... Explanation: Many corals secrete an exoskeleton that builds up to become a coral reef. An insect has a hard outer covering called an exoskeleton. Many corals secrete a hard outer covering that builds up to become a coral reef. That's why the answer is (H).

q: What forms when molecules react with one another?
Options:
- (A) biochemistry
- (B) Chemical energy
- (C) Energy.
- (D) atoms
- (E) chemical bonds
- (F) elements
- (G) flow of electrons
- (H) Organic compounds
a: (E)... Explanation: Chemical bonds form when substances react with one another. All substances are composed of molecules. Chemical bonds form when molecules react with one another. That's why the answer is (E).

q: Which has a unique water vascular system?
Options:
- (A) roots
- (B) trees
- (C) Conifers
- (D) Echinoids
- (E) fur seals
- (F) Most plants
- (G) ferns
- (H) bushes
a:
(D)... Explanation: Echinoderms have a unique water vascular system with tube feet. Another group of echinoderms are the echinoids. Echinoids have unique water vascular system was tube feet. That's why the answer is (D).